When I was a kid, my parents looked at each game, used the ESRB as a signpost, and let me play games that they thought I was emotionally mature enough to play. This continued until I was around 14 and their official policy was "anything that isn't GTA is fine," which is weird considering they let me play Mortal Kombat at the time (I think it had more to do with the perceived "realism" of GTA compared to something cartoonish like MK.)
Also, working at GameStop, I've noticed that a lot of parents are totally cool with violence, blood, gore, etc., but get up in arms if a video game has sex in it. I remember talking to a woman about wether Gears 3 was an OK game for her 8 year old son, which I said it wasn't on account of the massive amounts of blood, gore, language, and general nastiness in the campaign alone. Her response?
"Yeah, whatever, but there isn't any..."
"Yes?"
"You Know...*whispers* sex in it is there!?"
"I..uh...not really..."
"Oh, well all right then, it's fine!"
I guess chainsawing a man's head off is fine, but if there's side-boob? God help us.
God help us all.