Answer from Edwin Yuen, Microsoft Virtualization Expert:
Microsoft works with our partners like Citrix to provide solutions but Microsoft does have a comprehensive, Desktop to Data Center virtualization solution set.
I think MS is gearing up for something relatively big in the virtualization market.
The reason I think this is because of their current hand in virtualization–relatively limited. Also they have this software assurance non-sense which essentially makes you pay twice for a lisence and then another fee on top of this as a yearly charge.
The result is, you basically stay locked in to a non-virtual environment until Microsoft rolls out something big…and then you stick with Microsoft again.
Hope this helps!