Superheroes have themes. Very few of them have random assortments of powers, Superman being a rare example of this. For the most part, this is because every superhero, or supervillain as the case may be, has a theme, an idea, a unifying thesis. Spider-Man is a very clearly defined superhero in part because all of his powers center around his identity as the part man, part spider. 

A theme is an implicit boundary. It's a style, and all style is about saying what one isn't just as much as what one is. Spider-Man's powers are thus all about the abilities of a spider. Other superheroes are similar. Storm, of the X-Men, has the ability to control the weather, which is really a collection of powers in her case. Wolverine's powers are all reflective of a wild animal: claws, healing factor, etc. Even Batman, who has no "powers" per se, themes all his gear on the image of the bat.

Even superheroes who aren't on a theme usually have a single defining power. Superman's is flight. Sure, he's bulletproof and super strong, but flight is the thing everyone thinks of first. Supervillains also have defining powers, even if they have a theme that less clearly links them to those powers. Thanos, whose name comes from the Greek "Thanatos," meaning death, has death as his main "power," but that power comes from the Infinity Gauntlet, which gives him the power to do anything he likes. You may not be a demigod, a hero or a villain, but if you take this quiz, we'll tell you what your core superpower should be!