I'm wondering why it isn't called Microsoft Communication Foundation. Does it rely on Windows and will it rely on Windows in the foreseeable future?
I believe it's part of a larger branding strategy by Microsoft. For example, Windows Workflow Foundation and Windows Presentation Foundation are similarly not really tied to "Windows" as such, either.
(You could probably argue that WPF is "more" tied to Windows than the others, but Silverlight shows that much of WPF can be run on other platforms as well)