Well, I can imagine there's a lot of web designers who would love to take a shot at working on the physics engine for the next Portal game. Or play testers that would rather be actually doing development on the games. It would be interesting to see how people are cajoled into doing "lesser" jobs.

I imagine they have an endless supply of folks wanting to be play testers.

I suspect much of it is done by those of sub-employee status. But that's just a guess. Perhaps someone who actually knows will fill us in.