And also to be fair, XP is in a valid sense only one version out of date. Vista was a fiasco, and that's not just a meme -- Vista was released way ahead of schedule and still had a ton of known unresolved bugs. It was by far MS's most buggy release, and the whole thing was a disaster. Compared to the relative stability of XP, Vista was a step backwards. And while Windows 7 can rightly be called a newer version of Windows XP (and is better in nearly every way), it would be a stretch to say that Windows 8 is a newer version of Windows 7. Windows 8 is a fork into a different paradigm, and is so different it's not even comparable to Windows 7 along a number of dimensions.
All that said, XP is still pretty damn out of date, even with the latest service pack installed, and if Windows 7 is an option, it's usually a better one. Of course, XP uses less memory, so it may be suitable for particularly old computers. And for people that don't like to pirate software, owning a copy XP is a great reason to stick with XP (if it works well enough, why fork out the money for Windows 7?).