People are allowed to drink during gigs here in the US too. At my last show in Boston I came home drenched in beer and my ears ringing from the woman behind me screaming constantly throughout the show. It was so loud she lost her voice 3/4 ths of the way through the show (thank god) so I could actually hear the lead singer after that.

Some fans fail to grasp the fact that it's not about THEM (and their friends) - it's about whoever is onstage. If the audience is quieter here (and it isn't always) it might just be that they are actually listening to the music instead of expressing themselves.