Developing a WP7 app normally involves C# and XAML (for most UI layout). The frameworks include the usual .NET stuff, as well as Silverlight and XNA (MS's gaming/graphics) frameworks. A competent .NET or Silverlight developer can move into the WP7 development world comfortably.
I don't believe your comment about "dismay" is really accurate. I think Silverlight developers probably fall under one of two buckets: 1) "Cool! I can develop phone apps using my existing skillset!", or 2) "I don't really care about mobile development."
http://news.ycombinator.com/item?id=2644364
although it seems that was a bit over-sensationalized. I agree that at least reasonable SL developers will fall into your two buckets.
Microsoft is probably silent because they're not sure what technology the final project will use. Some exec could've ignorantly opened their mouth about "html5+js" and left the Win8 engineers groaning.
It'd pretty clear to me that .NET/Silverlight/WPF aren't going away. They are too popular and there's too much activity around those technologies.