Australia's Classification Board and their strict rating system isn't unknown to the gaming industry. Another title, F.E.A.R. 2, was refused classification for failing to meet the ACB's MA15+ guidelines. Once a game has been given this rating, it cannot be sold in Australia. In total, five games have been banned due to the RC rating in 2008.
A local Rockstar rep had this to say,
"Grand Theft Auto IV PC has been rated MA15+ strong violence, sex scenes, coarse language, and drug references by the Australian Classification Office. The PC game is unedited in any way and identical in content to the international version,"
So, congratulations Aussie PC gamers! You'll have your taste of the real Grand Theft Auto IV Rockstar intended you to have.
Source: GameSpot AU