http://en.wikipedia.org/wiki/Valve_Corporation#Games
That's not an insubstantial amount of games for one company.
This doesn't even take into consideration that they currently run the biggest online games store in the world which is a huge undertaking, and all the moonshot developments they have running that might not even see the light of day.
Valve are not a slow company. They're a savvy company. It's hardly surprising that they don't really have a flat power-structure, but they do seem to have some kind of structure that allows them to continue to innovate in a variety of areas.