I'm not so sure.
I am specifically aiming my game at 3g and 60fps; after-all how many people can/will update to Apples delegated min spec of 3gs within say the next 2 years?
I know Apple want them too :-) , because they like cash from new hardware sales.
But I always think there's a missed market opportunity when you don't cater for the min spec.
Of course it all depends on your app; 5fps on 3g would make most people cry at attempting to play the game :-))))
Depends on the app I guess

Cheers