Is there some strange law in Japan that states the a busty female character cannot be played by a busty woman?
They did the same thing with Cutey Honey, Mai Shiranui and Kasumi from DOA!
Every one of them was played by a FLAT (or practically flat) actress, when those roles could have easily gone to several busty women who would easily fit the required dimensions.
Ever notice that the porn parodies or transitions of hentai (Adult anime) usually get it right; except for Ogenki Clinic which contained a flat-chested Rukio.
IMO Japan's casting directors are really dropping the ball when it comes to choosing the female actresses for their movies!