It's a contortion to imagine Silverlight developers being happy. There's no point in building Silverlight web applications if they won't work in the default browser mode on PC's. So what was supposed to be a pervasive framework for rich web applications is now one of many for an unproven platform. This is such a heavy deprecation that abandoning it can't be far away.
I don't think you realize that Silverlight is XAML, WPF is XAML and Metro is XAML. It's all the same stuff.
With relatively minor changes we'll be able to run our Silverlight or WPF XAML in Metro and _continue_ to be able to run it the desktop browser (via the Silverlight plugin on Windows or OS X) or out-of-browser as a desktop app (on Windows or OS X).
To think that this is a deprecation is the contortion.
If you have every ported WPF to Silverlight you will know the changes are not minor. They are similar but the differences are large enough to make things very difficult in anything but trivial applications.
You also cannot share assemblies directly, which makes code reuse a big pain, no word on whether WinRT will support normal assemblies, but it's runtime is stripped down just as Silverlights is so probably not.
