More information regarding the Fallout 3 ban in Australia has come forward. While originally the exact reasoning behind classification refusal (which bars sales in Australia) was unclear, new details have emerged that point the finger at in-game drug use as the real reason.
Apparently, wanton murder and destruction is within the realm of acceptable gameplay for the OFLC, but drug abuse is not. Anyone who has played the Fallout series in the past knows that use of chems (drugs) in the game was quite common, amongst both the players and NPCs, and was in some cases an actual part of the plot. According to the OFLC, the real-world nature of the drugs in the game make them unacceptable.
Bethesda's answer may be to produce a censored version of the game to sell in Australia that meets local standards.