Someone pointed out on another forum I'm on that when Ang Lee's Hulk failed Marvel Studios went straight back into the studio and made a better one.
When Superman Returns failed it took Warners six years to get around to shaking their corporate paralysis and making a new one which may or may not be better. There's your difference right there in terms of flexibility of operation.
Marvel have a perfectly good JL-like cartoon in Avengers: Earth's Mightiest Heroes. Too bad the powers that be are canning it for another underage demographic show like Ultimate Spider-Man and Super Hero Squad.