Is it common sense?
I have to disagree that its "common sense" - many countries see the value of prohibiting minors from seeing certain forms of media based on content - Kids really shouldn't be playing games like Manhunt. This would have just given the parents the ability to say no - if they still wanted to buy it for the kid, they could have.
(Then again, Noone should be playing Manhunt - simply because it was a bad game - I have no problem with adults playing violent games)>
Adults (Parents) almost always get to choose for their kids (until they're old enough to make sensible decisions) its always been that way, and always should be.