Why are you being so unfair to WaW? It had a completely different set of weapons from MW...yes, it had to because it was WW2, but it's still a significant difference that had to be completely rebalanced. It added some more perks, changed the 7 kill killstreak, and tried to rebalance some of the old ones from MW that everyone hated(like martydom).
It also added nazi zombies which by itself made a lot of people buy the new map packs even if they never actually played the new maps, they just did it for more nazi zombies. MW2's advancements are not any more significant than these are, deatstreaks and the callsigns are cool ideas but in the end aren't significant to gameplay. Akimbo felt really tacked on along with Tanks in WaW, the next CoD could remove the feature and I wouldn't notice.
Oh, WaW also had campaign co-op which MW2 didn't even have.