Superman wears a cape because in most continuities, he uses it to protect others since it is made from invulnerable fabrics, thus allowing him to use it as protection from fire and bullets. He's also used it to create pockets for oxygen, during a fire, so that a person can breathe while he can get them out. Clark also has used it throughout the years to store his Clark Kent clothing, for when he's on the go. The other reason is that Martha had, in the previous continuity, thought that it made him look dashing. It doesn't provide drag since this is a man who is very fast and very strong. And very seldom does anyone grab his cape to use it against him as they know that you don't tug on Superman's cape.
To quote Edna:
November 15th of '58! All was well, another day saved, when... his cape snagged on a missile fin!
Stratogale! April 23rd, '57! Cape caught in a jet turbine!
Metaman, express elevator! Dynaguy, snagged on takeoff! Splashdown, sucked into a vortex!
**Sorry this discussion made me think of the incredibles.
Great response to any of these questions...
BECAUSE IT LOOKS COOL.
These aren't soldiers, these are superheroes and theatricality is the most important part of their costumes.
Secondary motion is pretty.
Proof is imminent...
Watchman, for example, did the "capes will get you killed in real life" thing too, but it made more sense there, rather than being a throwaway scene in which a character witnesses some of his friends die without any emotional reaction.
As for Superman, given the sort of power he has, I figure that the cape would tear off long before drag was ever an issue for him. Besides, if the cape is indestructible Kryptonian fabric, it affords him a useful shield for his more flimsy compatriots.
I think when you're strong enough to push planets around, your cape's a none-issue.
Pull List; seems to be too long to fit in my sig...