If you have worked there you would know...
Microsoft is like most big corporations. They have jobs for everything and to keep your job you have to justify its need. This is even more needful for "soft" science jobs like GUI design. Most if not all of the GUI work now for the OS is "make work" or real out there stuff of dubious value at least at Microsoft, the table top touch monitor comes to mind.
Unless they come up with something to do (like a killer app) for this who wants to be waving their arms around like some idiot all day?
The other fact is that Microsoft's long term goal is to keep all it's code on it's servers and rent it to us for use. When I worked there that was a major lament and now that the Internet is more than a idea it is possible. So they want the whole operating system to look and work like a web application.
Once you know these facts, you can understand the mess made of the GUI by Microsoft for its systems, like the abortion used on Vista and Windows 7.
The only really useful GUI-usability "stuff" is that being done on hand held stuff like the ipod.
