It's a joke anyway. I would never take the age ratings seriously. It has long been proven that video games do not make anyone violent. Such problems stem from far more serious issues, mostly domestically in the household. I was playing games like GTA and Duke Nukem 3D when I was a child and I am well-rounded. *twitch*
They do have an effect though on what shall we say are less educated, extremely impressionable young people. You only have to look at the London Riots to see evidence of that, people doing whatever they wanted, grabbing somebody and throwing them from their Moped etc...
While the majority of us who have common sense can happily play video games and watch violent films until the cows come home, there are those who don't and it has an impression on them.
Stopping kids from having content they shouldn't have until they reach the appropriate age isn't just done for no reason.
If for anything other than it would nice to not have to put up listening to 7 year olds playing Gears of War with their incessant whines, or young White American teenagers who like to refer to everyone as a N***** or a Jew.