.Net certainly adds alot to Microsoft's armada of software; but your right .Net is to allow Microsoft so they don't have to recompile thier libraries for each Platform.
It's not really an 'optional' move either, because Intel's IA-64 and AMD's x86-64 are very very different beasts; plus Intel have a response 64bit processor to the x86-64 which again is a new design.
So Microsoft are moving once again to those fabulous words
'IBM-Compatible'
x86, PPC to be more precise
Microsoft aren't allowing Apple to have .Net out of the goodness of thier hearts either; Apple want it so they can be 100% Windows Compatible, and Microsoft are getting a larger market.
Remember alot of the graphics industry uses Macintosh as they're more stable, reliable but most importantly the PPC is more powerful.
(not to mention Software developers find it easier to program for at the low level)
You might say here... Microsoft would be loosing thier market to Macintosh; but the old alliances of Microsoft and Intel are now dead. Microsoft have a multi-billion dollar deal; Royalties from every copy of MacOS sold. (MacOSX is around 1.5x the price of Windows XP Pro)
Also other Mac software which relies on .Net ... like Shake is planned to be (used industry-wide and extremely expensive).
Microsoft would also end up opening up thier Office to the Macintosh market, as well as a new games market.
And this isn't like it would be a great surprise to know that Windows 'Longhorn' will be PPC compatible as we already know that Microsoft had a prototype X-Box2 working with a PPC 605e Processor at one point. (Microsoft are not ones to use other people Operating Systems)
But don't expect this to mean DirectX games for Linux because of a Unix port. As i've said Apple will be paying quite alot for the use of this, Linux distro's can't afford that.
Apple will gain basically the entire Windows library of software and games to be able to use; meaning finally the computer industry will have made a 14year U-Turn and finally be back to where we were with Amiga, Mac and IBM-Compatible in the late 80s
Be bloody brilliant if Amiga finally release this damn Alpha machine!