The way I see it, there are three types of comic book fans.* There are those who read comics because they enjoy the medium, those who read because they like superheroes, and then there are those who are more concerned with collecting rather than actually reading anything.
Fans of the Medium: These people love comics because there is just something about them fundamentally that appeals to them. These are the people who only use "graphic novel" instead of "comic book." They've read Understanding Comics more than once. They have also read at least half of Reinventing Comics. Their pull lists always include Y: The Last Man or The Walking Dead, or both if they know that's good for them. They read some superhero comics, but they often restrict this habit to those written by Grant Morrison, Brian K. Vaughan and Niel Gaiman. They may not have read many Batman comics, but they can tell you exactly why Frank Miller's Dark Knight Returns is the quintessential Batman story. They also tend to be suckers for the Marvel Essentials line, in that they can get a motherload of comic for very little money, regardless of whether the stories are at all tolerable. Despite their obvious faults, these fans do have one thing going for them: when they bring a date home, they don't need to hide their collection of hardcovers, indie graphic novels and critically acclaimed manga.
Superhero Fans: These fans read almost nothing but superhero comics. They enjoy rich, and often times ridiculous, mythologies attached to their favorite characters. The best of them can name off at least ten members of the Legion of Super-Heroes. The problem they have is that anti-intellectualism seems to run wild in their ranks. They don't bother reading non-superhero comics because they think they don't like "smart comics" or "comics that make you think," even though I've told them to read It's A Bird a hundred times because I know they will love it! They also tend to get excited about things that are clearly stupid, just because they involve superheroes, like shitty movies or breakfast cereals.
The Collectors: Out of the three, these are the guys I just cannot understand. Rather than being a distinct group from the previous two, Collectors are a mutation of the Medium Fan and the Superhero Fan. Rather than buying comics to read them, Collectors buy them to have them. To see one, just wait at any comic shop on a Wednesday and wait for a guy to walk in with two dozen pre-boarded bags. Watch them grab every comic from every major publisher (regardless of quality or demographic) and place those comics neatly in the bags. Either these people are all rich or they still live with their parents, because it is insane how much money they drop on comics each week.
Of course, I'm not saying that people can't be a little of each, a lover of the medium and a superhero nerd. It's sort of like being gay or straight: it just depends on where in the spectrum to fall on. But in the case of Collectors, it's basically just sex addiction.
*Please note that I am restricting my generalizations to the American comics scene. I'm sure that the dynamics are different in other countries, especially Japan, where mainstream comics are more diverse.