That's a fair point . . . but, what about future games which will be Vista-only?
Arguably, Windows 98SE is a better choice for gaming than Windows XP, as it's faster on the same hardware and has much less overhead.
That doesn't mean that gamers shouldn't use XP though, the security reasons alone should tell you that.
Vista at the moment is not a great choice for most gamers, but when DirectX10 games become more common, it will become the platform of choice for enthusiasts wanting to play the latest games.