In India still a lot of companies and offices use XP.The upgrade will cost them a fortune both hardware and software upgrade.Since most of them are still on P4.My cousin's company Cybage still uses those P4 HP desktops and there are more than 300 of them.
So do all the little shops and the photo studio.
Even though you will be able to use XP but microsoft wont provide support for it and then what will be the point of paying so much for the software.
Before you make a purchase might I let you know that driver support for 64 bit XP was /terrible/. And the OS itself wasn't too stable. I don't think it even supports service pack 3?
If you ABSOLUTELY need 64 bit. Go with 7 64. While it is 7, I find it runs just as well as XP (when you turn off all the graphical goodies like aero). Plus you'll be able to actually find legit copies...