That won't fly. There are too many companies heavily invested in XP Pro. MS has no choice but to support XP for at least 2 generations if not more.
And I hardly think Vista counts as a generation for that matter. Windows ME certainly didn't. lol.
All that said I use Vista at home and really don't have problems with it. But I don't see my company rushing out to buy 20K plus licences for it either when XP works just fine.
For those who understand no explanation is needed, ...For those who don't none will.