Yeah, AO ratings are usually for games with sexually explicit content. Not ultra-violence alone, unless the violence were considered extremely distasteful. But even that might not pass for an AO. Look at the "No Russian" mission in Black Ops. Hell, look at GTA. Cutting a Spartan in half is nothing. Especially since in Unreal Tournament 3, players blow up into bloody meaty chunks if you blast them with a powerful weapon...