You're thinking about this in the wrong way. You're looking at re-releases of old games and wondering why they arn't on a new system. It costs LOTS of monies to make new games, and its not cheap to even translate/port stuff to the new systems. They won't take up all that much space and arn't really justifable to be put on disc. That leaves XBLA/PSN/WiiWare. Sales may/may not really make it worth the while to do.

If you're talking new games/IP's then thats a different ball of wax. The next gen systems can do WAY more than what a handheld can do, so even when you've got a console game thats being ported to a handheld, things have to change, and often its not good. I've got no desire to play Lego Batman DS, but will play the heck out of the console version. Same with things like CoD:MW. DS, no way, console, yes please. Those games just don't translate, or translate well.