I've gotten some responses to my question including a posting from Sam and some comments/email. So far the feedback has mostly centered on:
1- Deployment: It is much easier if you just need to deploy the framework.
I'm not sure I buy this. .NET makes it so easy to deploy an assembly like WSE that it really is no different from deploying any other part of your application. Even in a hosted enviroment, you can ftp the assembly to the bin folder of your hosted Web site. If you are deploying a new application that uses WSE functionality to 50,000 clients, you can easily deploy an assembly like WSE to those same clients.
2- Marketing: You'll get more adoption when you bundle features in the framework vs. package them separately.
This one I buy. Although applying more marketing and evangelism resources to a separate package such as WSE can mitigate the effect of this.
Ideally, the framework would contain all new features. Practically, it external packaging like WSE is not all that bad.