Two key reasons why Microsoft is proactively working with PC makers on new designs:
More than 80 percent of the revenue Microsoft generates from Windows sales comes from computer manufacturers who pre-install versions of the operating system on machines they sell. That sales channel was worth at least $10.5 billion to the company in the last fiscal year, according to Microsoft's most recent annual report.
"Apple Computer has shown that if you control the software and you control the hardware, you can make the two fit harmoniously into a beautiful, elegant package," said Don Norman, a former Apple executive who now consults with Microsoft and wrote the 2004 book "Emotional Design: Why We Love (or hate) Everyday Things."
See the article for more details (inlcuding some reasons Don Norman thinks Apple went too far).