It's unlikely we'll see many leaps in existing games (perhaps some sharper 3D renders and improved frame rates here and there) and any glitches in the move to 3GS will hopefully be addressed with the quickness, but as soon as developers get to tinkering with the 3GS's superior technology there could be an entire class of games that are unplayable on a 3G or, dare we mention, the original iPhone. Of course, doing so would essentially cut off twenty-some-odd million potential app buyers.
Needless to say, we don't think it's realistic to expect a ton of support for 3GS-only gaming until the older iPhone models are phased out. In the meantime, you'll have to stick to bragging about those blazing load times.
