Then Windows 7 will be even less successful than Windows Vista.
The simplistic truth is that migrating beyond Windows XP requires benefits - losing most modern legacy devices because you installed a new OS just makes no sense.
I find that to be mostly hyperbole. I've installed Vista on 8 computers and the only legacy device it wouldn't run was a web cam (because Logitech didn't create drivers for it). That's about par for the course - when I installed XP many years back, the only thing it wouldn't run was my favorite scanner (HP's fault).