If I were them, I'd keep artificially boosting it by whatever means necessary (pointless dialogue, etc.). The game sells better when branded with an M. Something about the exclusivity and seeming more "hardcore" I guess. The movie parallel works well here in that comparatively few sub-R movies are taken seriously for awards and whatnot. And this is all not to mention the extra advertising they get from "concerned parent" press upon release. All-in-all, most kids who want it will get it via their parents anyway, so the cost isn't worth the benefit of aiming it at a T audience.