If you don't relax, workout and enjoy the life part of life, then you probably aren't at 100% when you need to be. It isn't explicitly stated, but a lot of people I know agree with me. Some of those people are PhDs, doctors and other traditionally 'successful' people.

Valve has some of that written in, massages and whatnot. I think the key is that you have to be internally motivated to work at valve. They have to lay the social groundwork for people to be motivated without direct managers.