Originally posted by Juntai
It's because Superman is the most powerful reality warper in comics. The story forms around him.But yeah, even excluding that, it's pretty clear that being the most powerful man on Earth is just his floor, and he has many gears after that. He can be surprised and roughed up though before he realizes he has to hit the next level. Which is something he gets criticized for by his peers occasionally as well.
In a recent issue of Superman/Batman, Mxy even lays this out pretty clearly.