Yeah, Valve makes quality games and sells them for much lower than a lot of worse games out there. They COULD charge sixty bucks per game and still make a killing, but they make them 40, 30, 20, etc.

L4D2 has SO MUCH MORE than L4D! new characters, levels, zombies, weapons, better AI, and the game has only just been announced. Patching the classic L4D with all this stuff would take a very long time, and an x-pack would cost money AND require anyone who doesn't own the original L4D and wants these features to buy it.