My exposure to similar events is limited to attending NY Comic Con (which I was actually hired to work (and I was hired through a model staffing agency, compounding the weirdness of the situation)) and walking through a Star Trek convention in SF once when I had rehearsal right next door.

First, if working in the tourism industry has taught me anything, it is that, for the sake of mass producing a "special moment," the industry of event making must necessarily destroy some of what makes that moment special in the first place. In order to create a moment like getting to encounter your idols, you have to create a line and a room and a demand and a horrible, horrible Q & A line at the microphone. You also have to almost nearly kill that which you're marketing, just as you would mine a natural resource almost to the point of decimation only to back off in order to prolong how much of it you can capitalize upon.

I'm not entirely convinced that this is wrong or bad. The only reason why people are able to have a magical Alaska experience in, say, Denali National Park is because there is enough infrastructure to get into the park, just like Cons wouldn't exist if they were only built for small numbers of people. Everything is a business, most especially our dearest and closest religious experiences, because those things which are closest to us are the things for which we are most willing to sacrifice.

A brief related tangent: when I worked NYCC I was there at the behest of an agency that generally staffs models to do things like catering and event staffing. There was nothing model-y or glamorous about the job, except for perhaps the fact that we were getting paid $20 an hour to stand around with signs pointing to the registration desks. It was, though, interesting to see how the couple of nerds and myself in our little model/actor/musician group immediately bonded with the attendees instead of with our co-workers, and how little our co-workers understood the idea of arriving at the con at 4am to be the first to get in line to wait for another 4 hours to be in the front row to see Joss Whedon speak on a panel about the Avengers film. In that sense, my sense of community with the people there was sparked as a reaction against the people who weren't part of the "nerd group," and I think this holds true in society at large.

You're right, though, in recognizing that, despite shared interest, people still aren't friendly in the sense that they're going to start talking to you unsolicited. But then, I don't imagine you, Josh, were very forthcoming in sparking conversation with them either. I think a large part of community building is finding the smaller groups in the large; for the most part, this means being the only gamer in a society which doesn't care about gaming. But in a situation where everyone's a gamer, it requires being in a smaller sub-group which forces friendliness and community, because 70,000 people becomes too large a community to even count as a connected, interpersonal network.

All that being said, at both NYCC and the ST SF con I found people very friendly and open to conversation. People in costume were more than happy to take pictures and talk about their particular fandom and people with similar tastes did, by and large, end up connecting on some level at some point during the weekends. I think we have this false idea of the nerd community being this great friendly party where we all rejoice in how ostracized we've been growing up, but really, when it comes down to it, nerds are antisocial, so of course they aren't going to cultivate an outgoing friendly atmosphere, even at a con.