I think they restricted it after Beau and Janelle acting a fool in BB6. They still drink, but not as freely.
They only get 4-6 cans of beer, and a bottle of whine. (Among all of the houseguests.) They also only get it whenever production feels like giving it to them. If you watch Showtime/the live feuds, some people have been complaining about how they hadn't had any alcohol in like four days, specifically on the weekend.
Although this season there's a few people who don't drink anyways. I'd be pretty pissed though, as when you're couped up in a house like this with nothing to do, alcohol would probably be the best solution.