Win7 and WinXP are great.
I recommend Win7 when possible and Windows XP when required.
It's easy to tell if you 'require' Windows XP. Your hardware might not be upgradeable and you want to use the system resources for applications vs. the operating system.
For home PCs, Windows XP Media Centers are still running fine with hardware replacements. For some people, this is their TIVO, so they really don't want to mess with it when it's working.
At some point they might want HD, or they get Windows 7 on a notebook and are ready to upgrade to Windows 7 on their home server/TIVO system.
Anytime Microsoft or other parties (like commenters) start getting pushy, it's because they want to sell more product. Makes sense, but it's a buyer's market right now.