Perhaps they just need to clip a cutscene, or put proper clothes on a model. Often its a fairly minor issue that pushes ratings groups to make a title 'AO' or 'X' (if its a movie).
Its not like the game is a porno. It may well be, hell its even likely, that it would take a fairly small issue to get it back down to M.
Look at the GTA 'hot coffee' incident. Its not like the whole game was a problem, just one scene/mini-game.
There's no question the whole game deserves an M, but the AO content is probably pretty minor.