It's the same old story :

The claim :
With our new framework (previously VM) you could code in the language of your choice (previously Java)
and see it works without translation on any platform supproting our .NET framework
(previously our Java Virtual Machine)

The Facts :
It's as always the portable language myth (as old as ANSI C)used and abused by PR people to capt a market
that they'll hold captive later by introducing subtle change to make their portable framework incompatible with any competitor (as tilly already pointed out...).
Just add refurbished buzz words : ASP,SOAP (Instead of previous clients/server or thin clients...)
and you got a 'marketing killer Idea'.

My opinion :
Why not ? let's them developp all their stuff, there will be (as always) good things to pick-up.
But Let's not be naive to believe that Microsoft has suddenly changed its strategy
and has became an interoperability devot worrying about the developpers needs/desires.
Anyway, stay aware, and support open-source for it's the best way,
to my mind, to counter those silly tactics...

"Only Bad Coders Badly Code In Perl" (OBC2IP)