The thing is, AFAIK there are no other media which are subject to this law-enforced age limitation. The MPAA does its own policing, and theaters subscribe to it willingly. There are no law enforcement driven busts of theaters letting in 16-year-old kids into Rated R movies. There are no undercover police who look like kids busting stores that sell Parental Advisory music albums to elementary school kids. It's all self-policed.
This law puts videogames in a spot where they're lumped in with alcohol, tobacco, and guns. It's saying that a media, any form, can be as harmful as a controlled substance, or a weapon. And that's wrong. There's no dividing out one form of media for this kind of attention, and it is hugely fucking ironic that Governor Schwarzenegger, who rode into popularity on some of the most violent action movies of his time, is now pointing fingers at videogames.