and that's exactly what people are forgetting! But then they bring in their own excuses as to why the likes of Iron Man and Thor battled it out. Fair enough. The point is, a Norse God and a billionaire genius playboy philanthropist still duked it out with each other. What difference would a super powered alien and a billionaire with hi-tech toys having a little face off make?
sure it could work in a silly way, just like the avengers - but they tried to make MOS a bit more grown up. And batman certainly was.
in a grown up world i can't see batman and superman inhabiting the same universes without drastic changes to both.