Really, ISPs have the rules against servers because of the massive amount of traffic they generate.
However, PC game hosting is an entirely different animal. It is not going to generate the same amount of traffic for nearly as long.
I think the ISP companies are taking one rule (no hosting) and creating a blanket effect for everything that resembles hosting. That, coupled with their typical lack of computer knowledge, causes problems (I particularly like when they try to explain to me how Linux or Mac broke my internet, or is not network capable).
InfinityWard is to blame also. I know that all gaming companies are in it for the profits, such is Capitalism. However, most gaming companies know better than to screw PC gamers out of the things they take for granted any FPS game should have. Also, pricing it at 60$ to just gain an extra 10$ in profits seem ludicrous (The 10$ on console games are usually partly due to licensing costs).
Most PC gamers like control over what is happening to their computer. To some, having their computer host the game without permission is unacceptable.
