superman has endured as a character because he has grown beyond the original intentions of siegel and shuster. i mean, if you want to strip down the reasons for seigel and shuster's reasoning behind superman's creation, then it was nothing more than sarcasm and bitterness resulting from being sexually deprived. what does it take to get a chick? well apparently you'd have to have stunning good looks, muscles--hell, probably even need super powers!
but the character superman has grown and evolved and developed over the decades. and sci-fi is a necessity of the character, he is rooted in sci-fi. and it should be presented believably in his stories in regards to the universe these stories exists in.