If the demand is there, people will figure out a way to get it so a short term lack of suply shouldn't hurt overall sales that much, if at all. WaW Wii had well over one million sales. Not great by CoD standards, but far from bad (especially when you concider the lower cost of Wii development).
CoD5 sales were hurt by Activision themselves. Had Activision put the entire game on the Wii and made the game look better (the graphics were pretty bad), it would have sold much more. Maybe not 360, PS3, or PC levels, but still very well (probably closer to the two million mark). Now they are giving us a two year old game, and even though the game should be much better than the Wii version of WaW (better graphics, includes everything possible), the simple fact that it's two years old and there are no real screens, trailers, gameplay vids, or advertising means the Modern Warfare Wii sales will be, once again, hurt by Activision themselves. Perhaps they will get it right with CoD7, but I'm not going to hold my breath.