In some ways Dragon Con is the granddaddy of the generalist/multi-genre con as we know it today. Back when it started in the 80's, cons were still pretty specific to their niche. So a Comic Con was literally that, a convention about comic books. A sci-fi convention would just be sci-fi, etc. Dragon Con was different in that it had a bit of everything, and was able to kind of set itself apart in serving many different genres and flavors of fandom. So most cons you go to today are kind of following a model Dragon Con helped establish.
I will say though, Dragon Con's attendance has only really exploded in the last decade (before 2010, they were doing like 20-30k a year) and the crazy attendances of 70-80k have only really been in the last five years or so. So in their defense, they are still kind of new at running those huge crowds. As the con industry has exploded, so too have their crowds along with it.