I can see where the original poster is coming from. Video games are an interesting phenomenom, since unlike other "toys", it grows up with people and we've got people who have played every console from the Atari 2600 on, and continue to play them to this day. When I was playing "Combat", I could never, in my wildest dreams, imagine a game like "Metroid Prime" or "Resident Evil". And since I started gaming in 1980, I've seen the advancement in graphics and gameplay that games today offer over, say, "Pitfall".
Since the age of gamers has increased, it follows that the content of games would mature as well. However, I think that video game companies are headed for the same type of trouble that movie studios found themselves in a few years ago, but I don't think that it's all their fault. The movie studios were making R-rated films, and intentionally marketing them to kids and young teenagers, a group which shouldn't have been allowed into the films at all. There were many memos released that prove this. It's similar in the case of video games, but I don't think that companies have to intentionally market "mature" games to kids. The fact that it's a video game makes it appealing.
Anyway, what I'm getting to is this: Younger gamers crave "mature" games for the same reasons that we older gamers craved movies like "Nightmare on Elm Street" or "Porky's" when we were kids. They're "forbidden", they're taboo, and they contained things that our parents didn't want us to see. That's what makes GTA or even BMX XXX appealing to these younger gamers.
One of the many reasons that I bought a cube was that I was starting a family, and I've built a collection of games that I would have no problem letting my children see or play (except RE and Eternal Darkness). It's up to the parents to control and monitor what the kids see and play, just like it was back when we were kids.