This is a really "aggravating" topic and I do not know the answer ;-) I do know that I have been on both sides of the fence.

At a recent show where I was OP there was quite a number of SLRs present (and compacts and videos). My jaw hit the ground. I bit my lip and soldiered on. I could quite easily have packed up and left.

I suspect committees would not want to ruffle feathers and get exhibitors offside by restricting photography. I do not have a problem (if I am OP) with someone taking a couple of shots of their own dog or a friend but when it obvious someone is taking many shots or doing ALOT of filming for many 'friends' thats when I wonder. Do you say something or don't you?