The Australian government is finally
moving to discuss the possibility of legalising video games unsuitable for children. Currently, there is no 18+ rating for video games, with anything the censors find unsuitable for children either being banned outright or cut for the local market's prim sensibilities (for example, the graffiti-themed game Mark Ecko's Getting Up was banned for promoting illegal activity (presumably because graffiti is more plausible than running over cops and prostitutes or what have you), and one first-person shooter was knocked back because it included images of morphine syringes, and thus sent the wrong message about evil drugs).
Anyway, for what it's worth, the government's discussion paper on a R18+ rating for video games is here. It's currently a discussion paper, though I suspect that common sense will prevail and the 18+ rating will be added. Of course, Christian Fundamentalist groups could mobilise to swamp the discussion with arguments against, but the people who want to be able to shoot realistic zombies tend to be well placed to respond.