Comment My POV (Score 2) 245
The widespread use of pirated copies of the former and the latter's better security.
I attribute it mainly to the fact that Windows 7 by defaultt at least includes a basic AV software (Windows Defender) whereas Windows XP has none.
And don't mention UAC, please - most people either ignore it and answer YES to all its alerts or disable it altogether right after the installation.
And no, "pirated" versions of Windows XP (most of them are just a VLK version with a valid serial key included) have nothing to do with Windows XP security or lack of it.