I really think the ratings system needs to be changed. If a movie was released with the content of any of the recent GTA games it wouldn't even hit mainstream outlets. The game was not rated M instead of AO to keep it in Wal-Mart and Target,the "AO content" was removed to the ESRB's satisfaction.
When it comes to the sexual content, meh, I guess. I don't really ever get any glimpses of it because I always, without fail, skip cutscenes in GTA games. The stories (to me, anyway) are terrible, and never worth getting any mention ever, anywhere. The most fun I've had with any GTA games is trying to drive around a whole city without actually doing anything wrong. Seriously. If you can drive around Liberty City and not run a single red light, or get in a single fender bender, I tip my hat to you, because I can't.
On the topic of singling out sins, I really don't think it's fair to just settle on violence or sexuality. Almost every RPG out there has a core of occult content. If a sin is a sin, then to be fair, magic and spellcasting are like the pot calling the sex and violence kettle black. Just because one will bring about a less severe ESRB rating than the other doesn't make the T rated game any more appropriate in my opinion.
Just for an example into the ESRB's broken-ness, just check out Uncharted on PS3. That's the most realistic gun violence I've ever seen in a T rated game.