I certainly don't want to compete on price, but that can be a factor (a very big one when fully-burdened cost models are used - TCO).  Setting up internal SharePoint collaboration sites can be expensive, but adding in external collaboration sites takes it to a whole new level.  It also requires complex multi-server, mult-tier farms with elaborate replication and federated security.  This requires an investment in not just SharePoint, but Windows Server, SQL Server, search engine, security, email, replication, and a data storage farm.  Then each environment requires a decision about purchasing an 'Enterprise' license or the base server with user licenses (called Client Access Licenses, or CALs at $94 per user for SharePoint alone).  This is all before an organization can even begin to configure the environment for specific, optimized  collaboration themes for internal and external users.

So, let's add this up:

1. Company figures out how many internal and external customers will be using Sharepoint (good luck - especially with external)
2. Company buys multiple licenses for multiple products - mainly Microsoft (OSs, DBs, SharePoints, Web servers, email servers, security - probably Active Directory and a single sign-on server, search engine, and probably a replication product)
3. Company buys multiple servers
4. Company sends multiple engineers to multiple weeks of training for many software and hardware products
5. Company spends lots of time designing the server farm to accommodate internal and external collaboration needs, including development, testing, and staging
6. Company spends lots of time installing, patching, and configuring the environment
7. Company hires a collaboration designer to design, implement, and test all the themes, sites, sub-sites, directory structures, pages, widgets, and role-based security
8. Company develops internal documentation and training for internal and external rollout
9. Company has to maintain, patch, backup (and God forbid recover this complex, interdependent web of parts)
10. Company has to facilitate usage, adoption, and continue to expand the hubs and themes as collaboration needs grow

Is the picture becoming clear where the ROI is?  If someone is bent on doing a feature-function bake-off (which is a completely inaccurate way to perform a product selection process) - we will always loose since we don't have $8 billion to spend in R&D. 

At some point, a clear-thinking business executive will say - 'hey, I just want to share knowledge and wisdom inside and outside of my organization.  I don't care about all this other technical BS, and I don't want to pay a mountain of money for hardware, licenses and engineers'.

Here are some Microsoft blurbs on licensing and configuration.  Read the whole explanation if you really want a splitting headache.

http://www.bsgalliance.com/doc/show/247/conv/735

Licensing requirements

To host both intranet content and Internet sites, a minimum of two servers are required. This is necessary to satisfy licensing requirements. [JM note: this does not include all of the other software elements necessary to run a SharePoint site]

There are two server licenses available for Office SharePoint Server 2007. These licenses cannot be combined on the same server computer or on the same server farm: [JM note: see their 'farm' diagrams below]

Given the licensing options, the most critical design choice is deciding which farm hosts the Partner Web application. In the model, Server Farm A hosts the intranet content and Server Farm B hosts the Company Internet site. According to licensing terms, either farm can host Partner Web.

Given a choice of the two farms, general design guidance for determining which farm should host a Partner Web application includes the following:

In the model, Partner Web is intended for intensive collaboration with partner companies, including developing and staging the company Internet site. Placing Partner Web on Farm A allows the organization to optimize each of the two farms for their intended use (collaboration vs. read-only content).

Licensing requirements

Consider licensing requirements to determine the minimum number of server farms that you need to plan for. There are two server licenses available for Office SharePoint Server 2007. These licenses cannot be combined on the same server computer or on the same server farm. The following table lists and describes each license offering.

If you plan to deploy internal content for your organization and Internet-facing content for non-employees, you must deploy at least two server farms to meet licensing requirements.

The remainder of this section describes which license to use for different types of deployments.

Intranet sites for both internal and remote employees

Use the server license with the appropriate number of CALs. Even though intranet sites might be exposed to the Internet to allow access to remote employees, this is the correct license for this scenario.

Internet sites for external users

Use the Internet sites license.

Pre-publishing environments for Internet sites

In pre-publishing environments where multiple environments are used for development, authoring, testing, and staging, use the following guidelines:

http://office.microsoft.com/en-us/sharepointserver/FX102176831033.aspx

http://technet.microsoft.com/en-us/library/cc261995.aspx

Topology of the server farms

Each server farm in the model is composed of five servers with the following topology:

• Two front-end Web servers
• One application server
• Two database servers either clustered or mirrored.

The model illustrates the logical architecture of Office SharePoint Server 2007 by showing that:

• All sites are mirrored across front-end Web servers.
• The Central Administration site is installed on an application server to protect it from direct user access.

Partner Web

The Partner Web application hosts externally-available sites for secure collaboration with employees of partner companies. This application is intended for employees to easily create sites for secure collaboration. Key factors that drive design choices for this application include:

• Content isolation   Partners are not allowed to access other types of content hosted on the server farm. Additionally, with a dedicated SSP you can further isolate content by:

  • Scoping search to only the site level.

  • Not allowing navigation across site collections.

  • Not making profile data available across site collections.

• Separate authentication of partner accounts   Partner accounts are managed through forms authentication. Partner accounts are not added to the corporate directory.

• Permissions management   Individual site owners manage permissions to their sites, inviting only necessary participants to collaborate.

In the model, the Partner Web application is hosted by the same farm that hosts the intranet content.

Company Internet site

The Company Internet site is the company's Internet presence. The content is made available to customers by configuring anonymous access with read-only permissions. Key factors that drive design choices for this application include:

• Content isolation   Customers cannot access any other type of content hosted on the server farm.

• Targeted management   Authenticated access is provided for employees who manage the Web site, including administrative and authoring tasks.

• Secure content authoring and publishing   Separate site collections are hosted on Farm A in the Partner Web application for authoring and staging. This enables secure collaboration and content development with both internal and remote employees as well as with editorial partners who specialize in Web site development or content authoring. Content publishing is configured to automatically publish the content from the authoring site collection to the staging site collection (in Farm A) and from the staging site collection in Farm A to the production site collection in Farm B. The following figure shows the publishing process.

SSPs

An SSP provides a common set of services and service data to a logical grouping of Web applications and their associated sites. Services and service data include:

The most important criterion that determines if you need more than one SSP in your logical architecture is if you need to isolate content. For example, if your server farm hosts applications for more than one class of users, separate SSPs can help create isolation between these classes of users.

• Personalization services
• Audiences
• Business Data Catalog
• Excel Services
• Office SharePoint Server Search
• Portal usage reporting

The model incorporates a separate SSP for each of the following applications:

• Intranet
• Partner Web
• Customer Internet Web site