I think you guys forgot the word brief, or something.

Knights use to wear capes in pre early twentieth century American art. Maybe that's where it came from.

The Shadow uses a cloak, which is pretty much a cape.

However, is it part of a trench type coat, or is it literally tied at the neck or something? Didn't Sherlock Holmes wear a similar type of "over"? I don't know how to describe it.

In both cases, the trunks break up the color schemes and add some visual interest.

...and we're used to them.

Well put.  I agree with both Jim and David on this.  In a world where everyone is special, no one is special, and this became true of Superman more so than anyone else.

Since he's the template, nearly every defining element of his character and world have been duplicated elsewhere.  The one thing he used to have going for him against all this was that he was still the first.  Earth-One, Earth-Two, it didn't matter.  He was still the first.  Post-Crisis continuity retconned him into irrelevance. Yes, everything was supposed to "build up to him," I know, but it never came off, and his prescence as a central figure HAD to be endlessly discussed by everyone around him, because it couldn't be demonstrated in any other fashion. What was true about him was made into a lie, and that lie had to be constantly mitigated with further deviations and false praises.

All-Star works in part because he does stand on his own, in a world apart from all the other heroes and super-powers.  That book's reality is a fantastic, imaginative place, but in it, there is still only one Superman.