Singer left to do Superman Returns, but he was willing to come back to direct X3. FOX got Ratner instead.
20th Century Fox had been short-sighting Singer ever since the first movie. They gave him six months less time on a restricted budget for the first movie, they still cut his budget for the second movie requiring him to cut characters and sequences like Sentinels, the Danger Room and Angel, and for the third movie when he asked for a bigger paycheck (understandable since he delivered two excellent movies) and a bigger budget for the third Fox essentially told him to screw off (which is funny because X-Men: The Last Stand
eventually had the biggest budget of all the films, after Singer departed).
Singer abandoning ship to direct Superman
was as a result of poor management by Fox. WB offered Singer carte blanche with a big budget and creative control, something he didn't have with Fox. It's almost as if they thought they could keep Singer on a tight leash but that didn't last long. When he saw a better opportunity arise that offered more artistic freedom, like any creative person he took it.
As for Iron Man 3
, I'm really very lukewarm over how to receive this film. I figured there was going to be a third movie anyway but I was sorely disappointed by Iron Man 2.
Since the first movie was great, and there was rampant rumors of studio inference with the second movie, I'm hoping with The Avengers
finally out of the way Marvel can just let Jon Favreau make the movie he wants to make with Iron Man 3
and stay out of his way. Maybe we'll have a reverse scenario from what we're accustom to- the second movie sucks, but the third movie is actually decent. That would be interesting.