And as Win XP is no longer preinstalled on new systems, hardware makers will not write drivers for XP for those devices (because they are writing them for Vista).
Have you looked at the install base XP still has? Yes they are now and will continue to write hardware drivers for XP for a while. Heck I got Win2K drivers with some stuff I bought earlier this year. Manufacturers will make the drivers for versions of Windows they think will be on machines their users have.