Correct me if I am wrong but...
I think that were all focusing on pings in multiplayer a little to much. Low pings are needed for smooth gameplay but when pings are high the software uses it's best guess to judge where players are and what should be happening. When the game eventually catchs up it corrects all the locations and actions that are taking place. This is where you would see a player disappear from one location and jump to another.
Some games have better guessing software than others and if the 100 pings for mw2 are to be believed then I am going to say the IW.net might have some really good software behind it.
Guessing is still guessing, and the larger the ping the more guesswork is involved and the more you have to relax the hitboxes.
Thus making the game worse than smaller hitboxes on low ping