The $500 console(s) is designed for adults, marketed at adults (for our demographic) with related games for adults.
It is up to the adult to use parent guidance and keep the child away from such material. I think the problem is children get exposed to too much TV, and do not have a proper family environment, when the console becomes the surrogate baby sitter. Kids should be outside playing and tiring themselves out for an early nights sleep.
Unless it is a Wii or related device, which I can and do see your point. The simple answer to little Billy or Sally is: "no you cannot have that console, you are not old enough" or "sure you can have that console, just give me $500" which is the classic my parents used on me when I wanted a home computer. I wanted an Amiga and I got a CBM 64. The crack of " well Danny's dad got him one" would end up being very detrimental if I tried it. It would have been easier to get a puppy then an Amiga. So that would be the answer to the 12 year old problem.
The UK and EU have a good system. If you provide a game or movie to a child under age and get reported you go to jail, fined etc. What the parent does at home should be on the same basis.
Heck I don't particularly want one, even though I can afford $500. The 360 and PS3 still has some ROI, and the old consoles too.