Vista with the new security and other features expects to see more ram on a system since the new version is geared for boards that are able to run more memory. That's the fall back where OSs aren't keeping up with the much faster progression of hardwares. At first everyone was thinking ill and expecting game performance on the RC1 and RC2 beta releases and didn't get what they wanted there being beta.
The new games that will now come out written for XP/Vista over ME/2000/XP will be the ones that actually see any real performance. The current games out are too XP orientated. Yet older games like Return to CastleWolfenstein and Soldier of Fortune I+II seem to run will less problems on Vista for some reason. Figure that one out? They are less graphics intensive and use less memory on both system and video cards.