The other cons I've gone to have been either panel/discussion or role playing based. At those cons, the main focus is to engage in conversation or games. If there are "celebrities" they are often authors who write things, usually things I really enjoy, so it is a pleasure to meet them.
Comic con is mostly vendors, actors from cult shows/movies, and comic artists. There are a few panels, but it's not the focus. While I enjoy looking at the art and the huge amounts of stuff there is for sale, I don't know most of the artists and I'm not a collector and don't have the money to buy all the things. As for the actors, do I really want to stand in line to say "I really like the work you did/I think you're cute/I dressed like your character once." Not really. I think that most of these people are just normal people who were doing a job. While it probably makes them feel warm and fuzzy to hear it, and the $$ the fans are paying for autographs doesn't hurt, they often look kind of bored. And I don't really know what to say to them.
I realized that they are not "my people" in the way that some of the actors/musicians/writers/etc who I know are nerds/geeks are. Those are the ones I'm much more likely to fan-girl over. Because they are part of my culture in a way that goes beyond just doing a job. They are the ones that I could have a conversation with that goes like this: Me, "Geek." Them, "Geek." Me, "Geek geek." Them, "Geek nerd geek." Which is why w00tstock will always be way more awesome for me than Comic Con.
That being said, I did pay $ to have a picture taken of LP in his Jayne hat with Adam Baldwin (see previous post). I figured that that was special.