I noticed that at Hapden as well, so many people leaving! I mean fair enough people have trains/buses to get and maybe don't want to be stuck for ages after the gig's ended, but I just assumed that everybody knows that if a band is half-decent, they'll do an encore.
I also noticed a steady stream of people walking about during the show to get drinks/go to the toilet, which even if I don't personally do it (unless it's an emergency), but it gets really irritating in seating when the same people continually ask to get past you to get a drink or whatever. Especially in the middle of Richie's solo in DC