Mature does not equal violent. I volunteer with inner city youth, and all the male children play GTA, Modern Warfare etc, despite being 10 years under age. The kids go for violent games because they think their cool. The only people I know who play Wii are adult males who live on welfare and play games all day (hardcore gamers).
Just because a game is not brown with a ting of red, does not mean it is for kids (if anything its the exact opposite). I know most of you here are nine years old and may be developing high voices, but those "Mature" games are not timeless, unidentifiable from all the other fps, and expendable. I beat Kirby's Epic Yarn today, and I know I will play it again 20 years down the road, because I did for Kirby's Adventure (despite the title they are two very different games), do you honestly think you will play Modern Warfare after a year or two?