While I understand and somewhat agree with the logic of the doubters about nothing getting done without any management, I wishfully want to believe it might be true. Compared to what they have done and the money they have taken in, Valve is still an amazingly small company at 260 employees.
Small companies rock. If you can find motivated, talented people -- you can get amazing amounts of work done. My personal experience is the bad side of being a corporation starts creeping in at around 200 employees. At that point, you start getting too big to be picky enough to get the same kind of quality employees for every hire.
Maybe Valve has been able to maintain the small company feel up to 260 employees. Possible.