Here is a prime example at why Ign, like most mainstream gaming journalists, fail at actual journalism. They never bother to ask WHY single player is being ignored! All they can do is go "wahhh noone pays attention to the glorious single player campaigns anymore, it's all that damn multiplayer's fault!!!1 And you damn gamers!!!1"
Multiplayer is the REASON games like COD, and many others for that matter, are even relevent. Think about it, do you buy MW2 for the campaign?? Of course not! Online multi is the only thing keeping games afloat right now, so if anything it is keeping the industry alive! It certainly isn't "killing it."
I find it practically a chore to get myself through the campaign of Gears of War or COD, but hell, the multi in those games, I can go on for hours and hours. Yet I know some games like Minecraft, Fallout 3, GTA4, etc, I can't get enough of the single player. So why is it that certain games are like this?
The problem with single player campaigns these days (particularly FPS for some reason), besides the fact that they are generally too short, is that they are far too linear. They exist merely as a means for the developer to show off their graphics and story telling skills, even though they are usually pretty bland anyway. It cuts corners in gameplay scope and mechanics in favor of asthetics and horsepower clogging up all the room. The reason people respond much better to the multiplayer aspects is because it allows for much more freedom, which is what most gamers want anyway. After all, isn't that the point of games? Ultimate control and freedom?
Edit: I take it back about ign in this case, as they do seem to acknowledge a lot of the points I'm arguing. I just assumed the title "Is multiplayer killing the industry?" was also the title of the ign article. I actually give them props for daring to take on the mammoth that is MW and others like it. But again, I don't even think it is so much about the predictable AI as they claim, it's much more about the linearity and cutscenes.