The Australian Liberal party has long opposed an 18+ rating on games, but now with a change of government the debate has been reignited. The industry and many game players support the R rating as it would promote industry growth.

Many parent and family groups oppose the decision as they believe it will expose young children to obscene and overt violence in games. It must be rembered though that it would be against the law for under 18's to view the content and the responsibility is on parents and guardians, just as it is with film. (read more @ PALGN)

EDIT: IGN AUS has recently posted a fantastic article in the same vain as this (but much more detailed). You can find it here: R 18+: An IGN AU Perspective