I think it would be fantastic if all parents could find a nice healthy balance of being there and not being there. And, of course, it does depend on the kid.
Both my girls could be left alone by age 12, even 11 for a short period of time.
When I was 10 rode my bike with a bunch of friends to the beach every Sunday - it was a 13 mile bike ride. And then in the afternoon we rode our bikes back again, scorched and tired from being in the sun all day. When we got home, our moms made us shake off and change outdoors and jump in our pools before 'dragging in all that sand'. As long as we were home for dinner, our parents didn't give a whit where we were or what we were doing all day!
And we were approached by wierdos and likely sex offenders, but we knew to walk quickly away or not speak to them. We also knew to go or stay in a public place. We had common sense.
I think that helicopter parents rob their kids of the opportunity to learn common sense, street smarts, if you will. I look around and see these fledglings going off to college without a clue. And it's scary. More scary than a 9 year old riding the subway and learning how to navigate his way back home.
The only way to teach your kid responsibility for him/herself is to give it to them. Yes, it depends on the child. And yes, those of us with a difficult child ask ourselves the question all the time: When will he/she learn? When will he/she be more self reliant and more independent? But on a general base, I think that many parents could learn a lot from parents like the one in the article. First and foremost: Stop judging other moms/dads so darned much!!!