They do put slipstreamed discs online for MSDN, so I could go grab an XP SP2 install iso from there, and I'd expect to see SP3 ones soon. The main issue seems to be Microsoft doesn't release service packs often enough, and when they do, they don't tuck in all the drivers that they could.

I'd really like to see a 6-9 month max cycle on service packs. Installing XP SP2 fresh still requires over a hundred patches to be applied. Sure, hotfixes can also be slipstreamed most of the time, but a single service pack is much easier to deal with.