The other major system affected by this would be Windows 2000, for which
we already decided to not support it anymore.

WinXP (released August 2001) should be supported a lot longer than another year ;-) . It is still supported and installed on new systems.

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.