If I remember correctly, the companies will pay Capcom BIG bucks to make certain games (from big franchises) exclusive to only their consoles. Since RE has such a strong following, they expect people who didn't have the Wii to go out and purchase it to be able to play that game. It's a marketing strategy that unfortunately works. Nintendo had a contract with Capcom for RE 0, REmake and RE 4 to be exclusive to Gamecube, and I remember something about Nintendo taking Capcom to court when RE 4 was ported to Playstation. Who knows.