It's easy - Facebook is all about voyeurism. And when you can no longer get your fix from Facebook stalking your friends, you move on to the next thing. Purely conjecture, of course.
Totally agree on the commitment to the whole .Net ecosystem, but that is a feature, not a problem, because for the most part the various places play very nice together - so nice in fact that we have time to actually COMPLAIN about this integration :)
Another minor point is that yes, MS has higher licence costs for sure, but the other expense for a business is the development time themselves. A .Net developer can quickly switch between WinForms/Web/Mobile/Silverlight(for what it's worth) with very little learning curve and all within the same IDE. I believe it gives a business many more options without needing to bring in and train specialists.
Yip for sure. It's too much to explain in a forum, but I've been meaning to post an article on how I've been using these technologies together. If anybody else is keen, just post a comment on the blog and then you'll be alerted when it's ready.