I found something about the wii version of COD4
I watched a video on gametrailers.com, and they said that if they did make a wii version of COD4 (and they might), it would be a different story in the same timeline as the other COD4s for the 360 and PS3.... and the only reason a wii version of COD4 wasn't being made was because without HD graphics, a COD4 on the wii wouldn't looks so good
So what i think is that they will probably make a COD4 for the wii but it will be an exculsive storyline that the PS3 or 360 versions won't have...
They did this with a few other games like Splinter Cell DA