Actually, if I recall correctly, Valve stated that their entire staff are separated into different projects. If my assumption is correct, that means that they’ve constantly got people working on every project they’ve got, including maintaining DoD and CS.
Team Fortress 2 has a dev team, still (made clear by all the hats and Walker’s shenanigans), Portal 2 (obviously) has a dev team (which is probably the busiest team right now), Left 4 Dead has a dev team (the DLC’s and such), and I’m positive Ep3 has a dev team (probably had one since the 1800s, too).
Saying that the company is dumping shit tons of resources into one project is flat out retarded. No company is that dumb, and Valve is by all means a very sharp company. They know what their doing.