This is lame, but absolutely confirmed. WiiHD got the word direct from the mouth of the Call of Duty: World at War developers, Treyarch. Even though Call of Duty: World at War is going to be a game heavily intended to be played in four-player online co-op mode on just about every other platform it ships for, the Wii version is going to be neutered down to two-player local co-op. When games like Brawl are offering perfectly functional four-player online play, this just doesn't sit well. Here's Treyarch's statement on the issue:
We are proud to bring what we believe will be the best-looking Wii game this fall to the community, but that comes with technical trade-offs. The difference between competitive MP and co-op is non-trivial. Think of a size of an MP level, then compare that to an SP level. Then consider all the AI code, level scripting, and endless other content in a SP / co-op environment that is just too much for the Wii to sustain with our engine.