What core technology - XAML & .NET ? AFAIK WinRT is a rewrite and is not compatible with WPF & Silverlight. Silverlight (cross-platform RIA plugin) seems dead.
Certainly Win8 and Windows Phone are not binary compatible with WPF and Silverlight but if you wander around the portion of msdn dedicated to Metro apps or to phone development and look at the available types and methods from the core runtime up to the presentation layer you can see that the common overlap is very large and that they probably started from the same place.
So the namespaces have changed, but the techniques remain the same. XAML remains the same. I can't imagine anyone expecting their WPF application to compile for a new interface with different metaphors.
Forget silverlight, .net itself has a questionable future on windows client. WinRT went back to C++. .NET is being positioned a server side technology.
It depens on what you consider .NET. The CLR? The .NET metadata schema? C#/VB? The only thing that isn't incredibly important in WinRT is the CLR proper. But the other aspects of .NET play a huge role in WinRT. They even went and largely reimplemented the BCL. And the API design guidelines across the board are .NET based. WinRT looks a million times more like .NET than Win32.
But to your point, I'd wager that .NET is already used more on the server side than on clients apps as its use in enterprise line-of-business is massive.
