There's another thing in XP's favor that I forgot about. In the early days of XP, there were a lot of posts on how Win98 was more backwards compatible, as it was still basically a GUI running on top of DOS.
I have some old DOS games that I could never get sound to play through the PC speakers under Win98 on b/c they were only setup to use the internal speaker or a Roland or Adlib soundcard that none of the modern integrated sound chips emulate.
Then I discovered DOSBOX - a full 80386 DOS PC emulator that yes, only runs on XP, and also emulates the PC speaker so it's output is routed through the internal sound card.
In summary, with the exception of some glitches with After Dark the screensaver, there is nothing that I can run on Win98 that I can't run better on WinXP, but there are more and more apps that work on WinXP and not Win9x.