The Classification Board is the body responsible for rating video games (and other stuff!) in Australia, and as such, is often blamed for the mess our system currently finds itself in. Thing is, it's not their fault.
The Board's job is to look at a game, assess its content, then award it a rating. That's it. The decision to add an adults-only rating for the country's games rests with politicians, not this apolitical body, something a representative from the group is able to explain in great detail as part of this interview with AustralianGamer.
The unnamed rep, revealing the Board's methodology under condition of anonymity, goes into great detail about how a game is rated in the land without an adults-only classification, saying most games are played to completion by staffers, and those that aren't are classified on the basis of video footage and a description provided by the publisher.
Of particular interest is the Board's guidelines on what constitutes excessive violence, which was the reason given for Aliens vs Predator's initial ban: