When we introduced .NET, people made the assumption that COM and Win32 were dead (even we did, as Longhorn proves...). Remember that?
WinRT does not equal the demise of Win32. It's a new thing, yes, and it's aimed squarely at realizing mobile, touch-first computing experiences on latest gen Windows powered devices. Win32 is not designed for touch-first computing, right?
Win32 is alive. COM is alive (they are the glue of WinRT, forming the basis (the kernels) of WinRT's programming and execution models).
So, yes, the desktop is older than WinRT, but this doesn't mean it's no longer relevant. Win32 powers WinRT (and COM itself has evolved to meet the needs of the new model...), in fact ( WinRT is built on top of Win32, which is, as far as I can tell, still the de facto programmable OS layer for user mode Windows applications and services...).
By the way, what makes you think Microsoft thinks that WinRT is an "out" from the Windows desktop? Can you elaborate?