In order to get back into the habit of writing, I will once again endeavor to write 100 words in 100 days.

Why would a real superhero attend a comic con?
Real superheroes are those persons/beings who have super powers. Super as in supernatural, not normal, beyond human. This power is either natural to them, derived from an outside source magically, chemically, or mechanically. For example, Iron Man is a superhero with a natural intellect that is superior to most humans and uses a mechanical aide to help him do things that normal humans cannot, such as fly and shoot bursts of power from our palms. Spiderman is a superhero who started out as a normal human and then was chemically enhanced to by the bite of a radioactive spider. The Hulk was chemically changed by gamma rays, as was Captain America (or at least, that’s what I got out of the Avenger Movie).
So, why would a real superhero attend a comic con. I say he or she would like to blend in. Where else could this person dress up as they want (in a spandex body suit wearing a mask) and not have anyone notice them? They could meet other real superheroes there to discuss their business (saving the world).
Another reason a superhero might want to attend a comic con is to meet the actor who portrays him on TV or in the movies. That might be interesting. Maybe the superhero is bored. Maybe the superhero is checking on the super villain.
Not only would real superheroes attend a comic con, but I think real super villains would too and for similar reasons. Only the super villain would probably try to destroy the comic con in some manner. Jealousy of too many people dressed up as the superhero, perhaps. Not enough people dressed up as villains? Maybe the super villain would want to interrupt the yearly meeting of the real superheroes, like crashing the party.

Update (1:07pm):
Perhaps the superhero is stuck. His/her special powers are limited by some gadget that the super villain has hidden at the comic con. She/he has to go to the convention, pretend to be a normal person, find the item, and recover the item without coming out or being discovered by the super villian (who obviously won their last encounter). And of course, some normal person finds/purchases/has the special item.