TreyArch made CoD: World at War and CoD3, Infinity Ward made others. I think.
This statement is true.
TreyArch made CoD 3 and CoD: World At War. (For the 360)
Infinity Ward made CoD 2 and CoD 4. (For the 360)
I'm not gonna take sides and bash the other one, even though I personally prefer Infinity Ward. But people have criticized TreyArch because of the changes they made to CoD 3 that they thought didn't make it as good as #2, so people were mad when TreyArch was making WaW.