I actually made a post about this last night. I'm quoting it here for my argument because I'm lazy.
Originally Posted by SuperFerret
I confess that I hate when people confuse "realistic" with "real". "Realistic" is just something that seems real, but isn't. Honestly, "believable" is a far better word, and takes into consideration the fictitious nature of the world being presented.
For example, take Superman's world and Batman's world as separate entities (not part of the DCU). Superman is inherently more believable because the basis of his world is that there is a god-like alien that exists. Thus all the funny little oddities, such as nobody recognizing Clark because there's no way such a meek guy could possibly be a god-like figure (plus Superman doesn't wear a mask, so he probably doesn't even have a secret identity to reveal) just fall into place and make sense. Batman's world tries to mirror reality, and it does so, aside from the glaring fact that it's near impossible for someone (even someone as wealthy and dedicated as Bruce is portrayed) to be that adept in so many diverse fields while also being fairly young. Batman might be more "realistic" than Superman, but Superman's unrealistic nature makes him and his world more believable.
I hope that made some sense, as it's 2:30am and I'm going to bed.
Basically, Batman's "realism" makes him less believable, while Superman's "unrealism" makes him more believable.