Re: but there is also the stadium effect?
There are a couple of ways to approach this, and I've witnessed one firsthand:
1) The stadium approach.
Yes, there are loads of people. So, they use specialized, directional antennas, crank down the power, and place shielding behind and around them to limit the signal. Works for the superbowl, generally held at only the largest of stadiums!
2) The conference approach
This is the one I've seen first hand. Xirrus makes a line of AP's that effecitvely have like 16 radios and antennas set up in just the way described above; they are arranged in a circle, are highly directional, and have shielding to prevent leakage. NANOG uses them to handle their summer keynotes with generally 1000+ attendees in a room. I think they usually have 4 of these in the room. Naturally, these are fairly bandwidth hungry users, as they're all net admins/architects/operators/engineers with generally multiple devices on at once. It's quite a feat to have witnessed.
For a venue such as Hofstra, approach 2 would probably have been best considering the likely limited skills/tooling of the tech on hand, though I'm sure the bleachers would have made things difficult either way. I'm kind of surprised they didn't just ask a vendor to come in and essentially advertise their gear by operating the wireless just for this event.