The new content in the "Extended Cut" of The House of the Dead: Overkill has resulted in the game itself being cut from Australian release. The Classification Board has refused classification of the PS3 update of the Wii game. The R18 rating has yet to go into effect, meaning that material considered too "adult" is still refused classification.
The original potty-mouthed zombie shooting game was released in Australia in 2009, though there was some controversy at the time about the rating lacking notification about the vast, prolific use of profane language. Perhaps, then, it's not that this version is much more objectionable -- it could just be that the board wasn't paying close enough attention the last time.
We've contacted both Sega and the Classification Board to learn more about the (expletive) situation.