Just throwing my 2c out there, but the idea behind the R18+ wasn't so much as to allow games of a higher level of violence into the country, but to make sure that any games not suitable for younger audiences don't reach their hands.
Having worked in both retail and IT, the mentality of parents is "oh, Billy is 12, and this is only a 15+ game. That isn't too bad for my little angel" (Yes, this is just about word for word what a parent said), but as soon as you whack a 18+ ADULT ONLY rating on something, it becomes all "protect my boy" and "how DARE they market this to MY child" (Again, things parents have actually said).
The point is, perhaps there are things in SR4 which are just a bit too far into the morally wrong field. Should we be able to choose for ourselves, as adults? Probably. Should said adults be able to recognize that this content is socially questionable? Probably.
However, in the current climate of Sexual Harassment, Rape, Murder, etc of women, one cannot blame a classifications board for saying "hmm....this doesn't help with resolving the issues in society". Again, does a game cause someone to become a rapist or murderer? Probably not. Does having a game which depicts violence, sexual or otherwise, help society? Probably not.
That's my 2c, not much, but something a squeezed out.