For many people straight out of school, this sort of environment can be very appealing. They get to work on stuff they like to do anyway, the free perks are better than anything they could get themselves (food, game room, etc), and the majority of their friends and relationships happen through their work environment. Since they don't really have much of a "normal" life yet (no family, etc), work _is_ their life. It's a bit like still being in college, but getting paid.
Eventually, most of these kids hit 30 and start a family, develop priorities outside work, and so on, and realize they need to move on. But there's always a fresh crop of smart 21 year olds ready to take their place.
At first that was my thought too. Who want to live at work. But if you took me fresh from getting my BSEE and I could work at Apple 80 hours a week AND get paid hell yeah I'd take it.