Kotaku Australia has follow-up on reports that Fallout 3 has been banned in Australia (story), providing the OFLC's official report on the action. In short, it was not any violence or gore in the game that triggered it's banning, which was based entirely on the game's depiction of drug use. Here's the relevant quote from the OFLC report:

The game contains the option to take a variety of "chems" using a device which is connected to the character's arm. Upon selection of the device a menu selection screen is displayed. Upon this screen is a list of "chems" that the player can take, by means of selection. These "chems" have positive effects and some negitave effects (lowering of intelligence, or the character may become addicted to the "chem"). The positive effects include increase in strength, stamina, resistance to damage, agility and hit points.

Corresponding with the list of various "chems" are small visual representation of the drugs, these include syringes, tablets, pill bottles, a crack-type pipe and blister packs. In the Board's view these realistic visual representations of drugs and their delivery method bring the "science-fiction" drugs in line with "real-world" drugs.