Team Fortress 2 came in the Orange Box, which was 3 games (4 if you count episode 2) for 50 bucks, easily 20 hours of gameplay, plus a lot more if you really got into TF2. The Orange Box was pretty awesome, but that is in the past and has no relevance.
L4D comes out - 50 bucks, maybe 4 hours of gameplay. And a year later, L4D2 comes out - also presumably 50 bucks. You call wanting to not buy the same game every year being "stingy?" How about they put forth a little effort in the creation of that first game. It's shorter than the original Fable, for God's sake.
And people need to stop comparing L4D2 to the WOW expansions. First, Burning Crusade and Wrath of the Lich King came out almost two years apart. Second, they weren't full price. Third, if you stack the content in Burning Crusade or Wrath up next to Left 4 Dead, L4D would get lost in the shadow, never to be heard from again. Fourth, Blizzard actually supports their products and releases new stuff all the time, and don't tell me it's because of the subscribers. If Valve wanted to have a subscription service so that they could actually give people stuff, I'd be all for it. Maybe we could get a new version of Steam that doesn't suck.