You really don't want to run iTunes on an 11 year old PC. Even if you had a powerhouse PC back then, it will be too slow to handle iTunes. Syncing may take hours. Remember, those pc's didn't have USB 2.0.
why do you care? XP sucks compared to Mac OS X. Itunes wants a minimum OS on the Mac because of how it integrates with the other parts of the OS like iCloud and such.
This is what it basically boils down to, the more people you support with the same system the more issues you get. If we all used the same computers these companies would have a much easier job.