If only it was that easy. Kids addicted to games that aren't 9 years old and totally under parental control just do what they need to to keep playing. Some games are like crack to some kids, and they will go to crazy extremes to play.
Maybe if you get in front of it, stay totally on top of how much they are playing and status of homework and chores, and stick with rules on use before they lose control, but I've seen too many kids that just can't stop, and the games means more than anything else to them.
I didn't say it was easy. My kids are 8 and 4, they get to play games, and since it's summer they get to play more games. During hte school year it's limited time after homework and dinner is over. Even so, they spend hours a day in a swimming pool, outside, etc...
For many parents it will be a challenge that's damn near impossible to overcome. With two parents working (assuming there's two parents invovled) just to make a "middle class" life, it's unreasonable to expect those parents to have the time and energy to even fight with their kids about it.
For me, if my kids grades were slipping because of video games, it would be unplugged until the grades improved.
Everyone's situation is different, and if video games get to the point like you're stating....then it's time for rehab. I'm definitely not doubting the addictiveness of video games, as a younger dude I struggled getting away from Quake 3, and moreso UT99, I was hooked for almost 3 years. I had to go cold turkey for a while, and never went back to those games.