For decades, Microsoft's strategy has been to protect sales of Windows and Office at all costs. Those are the company's revenue and profit centers, and Microsoft's inability to make money online or with its consumer electronic business has made protecting Windows and Office a self-fulfilling prophecy--they need to protect their cash cows because they can't build new ones.
I'm one of those people who's still running Windows XP, because Microsoft is basically requiring XP users to "forklift upgrade" if they want to go to Windows 7. I run Windows 7 on my netbook and it works fine, because I was able to start with a bare machine. I've used my current XP system for four years and shudder to think about buying a new system and reinstalling software from scratch.
There are a lot of people in the same boat, but Microsoft is showing all of us the friendly middle finger. The trend started with experimental products like Pivot--sorry, but they only work on Vista or 7. Yesterday, Microsoft made the Windows Phone 7 Series SDK available for free download, but even though the instructions say that it'll work on Windows XP, it doesn't. The installer demands Vista or better. Then, Microsoft released the preview version of IE 9, and again, it requires Vista or 7.
If I was so motivated to get a new system and reinstall all my software in order to use these new Microsoft products, I'd do it, but I'm not, and I don't see anything there that would justify spending either the money or the time. I'll happily continue working on Android on XP and the iPhone on my Mac. The Microsoft Office team was able to figure out how to get Office 2010 to work perfectly fine on XP. Microsoft should be looking forward to build new user bases and new businesses, not backward to protect Windows revenues at all costs.
Update: I've come up with a personal solution, which is to install Windows 7 under Parallels Desktop on my iMac. It seems ridiculous that my most economical solution to Microsoft's "push Windows 7" strategy is to run it on a Mac.