Ryan North of the webcomic Dinosaur Comics asked his friend Ben Tippett to write a formal paper explaining the coherency of Superman's amazing powers. It's a very math and physics-heavy article, so I won't try to understand, let alone summarize the whole thing. Here, however, is the conclusion:

We conjecture that all of Superman's powers come from His ability to alter the inertial mass of objects in His immediate vicinity or with which He is in personal contact; although the mechanism is unknown.

Link via io9

Image: flickr user chanchan222, used under Creative Commons license.