Comment We do know why it was refused classification (Score 5, Informative) 166
A copy of the OFLC Board Report on Fallout 3 can be found at Australian Gamer.
Basically, Fallout 3 has been refused classification because the majority of the Board consider that the use of "Chems" and specifically the Morphine chem to provide advantages in combat contravene the National Classification Code.
From the text of the report it appears that renaming the Morphine chem to 'Painkillers'(or some other generic name that is not a prescription drug) and changing the icons presented in the menu for selecting chems will be sufficient to get the game classified MA15+.
I have no idea why Fallout 3 has been singled out like this when other games such as Max Payne, Bioshock, Haze and the original Fallout games all have similar drug use.