Not everyone is as familiar with the origins as you think. Origin movies are a good way to get a new generation of fans interested in the character. I was too young to read comics when I first saw the Donner Superman movie. That was my introduction to the character's origin. I know it now, but I didn't when I first saw it. People like you and me take it for granted.
Indiana Jones. Huge hit. No origin movie.
the Incredibles. Huge hit. No origin movie.
James Bond series. Huge hit, beg. with Dr. No. No origin movie until Casino Royale.
A good movie, even a good fantasy-action movie, doesn't need an origin to suck people in.
And lots of people become "new fans" of superheroes without the origin being the first thing they see or read. You may have not known about Superman until you saw the Donner movie, but a lot of other people got into Superman because of picking a random, non-origin, issue of the comic book. Or by watching a random, non-origin, episode of the George Reeves series. Or watching a random, non-origin, version of Super Friends.
Also, forget the movies for a second and look at the Batman TV series. Campy or not, it was one of--if not the--most successful adaptations of a comic book superhero of all time. Hell, people still quote the "biff pow zap" stuff and imitate Adam West. It was a huge hit upon its premiere. It made an entire generation of kids into Batman fans.
And there was no origin episode. No Thomas and Martha Wayne. No Joe Chill. No Crime Alley. No bat through the window after twenty years of training. Nothing. All you had was Bruce Wayne making a brief mention to the Wayne foundation board that he was funding an anti-crime initiative because his parents had been murdered. Then it was to the batcave, roll credits and kick the Riddler's ass. The producers knew that all you needed was a brief snippet of back story and then instant action.
Furthermore, at the time the series aired, Batman wasn't even that popular. The book was almost canceled. And the origin was only mentioned in the comics once every five or six years (if that).
Therefore, you can't argue that the millions of new fans that show created already knew the origin. Or that they needed the origin to enjoy the show.
If Batman can be successfully adapted once (and, using the terminology of today, "rebooted" from the movie serials) without retelling the origin, I think the same could be said for Superman.
Frankly, Superman could use a reboot with an origin movie. One, it would separate him from the lackluster Singer movie. Secondly, it could redefine a him for a new generation. I likes me the Donner Superman movies, but I'm not a fan of his vision of Krypton. I'd like to see a new, big budget version of Krypton.
So, really, it's just a matter of personal preference. You'd like to see another origin. I'd prefer something else. Beyond that, we're both speculating on the need (or lack of thereof) for an origin movie and how successful it might be.
