You sir have come to the right place. Well sort of. There are better places for discussing this, but you at least have the eye of someone that is very much into all things superheroes. That would be me.

My RPG of choice is the Hero System in fact, and you would be hard pressed to find a better system for handling Supers. Yes, M&M is great as well, and there is constant discussion comparing the two so lets not go there.

Anyway, to address the question at hand, you've stated that history won't really be affected very much because of even distribution of the supers. Assuming that we are sticking with Earth as is, that doesn't mean that there would have been some changes here and there to the physical geography. The question really should be just how powerful are the supers? If supers range through the cosmic power range, than there is no reason that Moses (a powerful telekinetic) couldn't have diverted rivers, pushed down mountain ranges or widened rifts.

Personally the whole alternate history thing has become so common these days that it really isn't unique anymore. Don't get me wrong, I love alternate histories, but they can get a bit forced some times. I think your idea of having very few changes to outcomes of wars and such is actually more unique and certainly easier to write about as you can easily do cause and effects with the super interactions just maintaining the status quo.

I'll be watching this thread with great interest.