I think if we're including PC in the conversation, then basically no game is exclusive because you can always play console games on emulators on the PC. I don't think there're emulators for the next-gen systems yet, but I'm sure they'll come soon enough.
In the context of arguing about game exclusivity, I think most people just refer to game consoles and not include PC. Otherwise M$ fanboys can't claim that games like Halo and GOW are Xbox exclusive.