Forgetting that for a moment, I'd thought that Singer was going to go for the angle where, after meeting three others from Krypton in SII, Superman felt the need to see if there were other survivors. That could have made a good catalyst for why he left.
If Jude Law wasn't such a prick, maybe Zod would have actually told this to Superman. Apparently Singer wanted Jude to play Zod, and when he woudn't commit to the part, Singer dropped Zod altogether rather than find another actor (James Marsters -- not Marsden but Marsters -- anyone? Wayne Pygram?).
That would have worked wonders. Lex and the now-mortal Zod hatch a new scheme to rule the world. Zod tells Kal-El there were survivors from the big bang. Kal-El leaves on a five year wild goose chase, leading us to the movie we saw.
Anybody catch who the old lady that Lex scammed was?