I'm not quite sure where you got $600 from. There are plenty of legal ways to get vista for free (I use the MSDN-AA, but another way is to find a friend with it pre-installed who wants XP, let him install xp with your key and you install vista with his).
If you meant the GPU, I'm sure the bulk of people buying dx10 cards are doing so for their excellent dx9 performance or video decoding. Since you're going to upgrade eventually anyway, you may as well get a dx10 card when you do.
Oh yeah, nobody is FORCING you to do anything.