SimonG: So in the COD situation, not buying any overpriced map packs should get some attention.
Navagon: I reckon it's a bit late for that. By removing the possibility to mod the game Actiblizz have starved the players of content to such an extent that they'll ravenously consume all the overpriced map packs they put out there (rather than you know, move onto a different game).
Don't forget about Call of Duty Elite! By paying 49.99USD (if I recall correctly, that's per year), you'll get all the 'pro' features you need to p0wn the competition, get double XP if you're in a clan, get all the latest Elite features, get complementary DLC every month (which becomes tied to your PSN/XBOX Live account, meaning you keep it even if you end your premium subscription), and more!
In other words, Activision-Blizzard is well aware of this, and, through the unanticipated success of the Elite service, has managed to capitalize on it very well.