WinXP (released August 2001) should be supported a lot longer than another year ;-) . It is still supported and installed on new systems.
The other major system affected by this would be Windows 2000, for which
we already decided to not support it anymore.
Good catch. Windows XP, according to reports online has somewhere between 50-75% marketshare of all personal computers in the world. The Vista fiasco has created a large void which is only now starting to get filled with Windows 7, but it will yet take a long time to dethrone XP.