New York has a walking and transit culture similar to Tokyo. Yet most New Yorkers would not feel comfortable sending a six year old out alone. I don't think walking and transit use is alone responsible for the difference.
That's more or less where the similarities end
Seems like that event and the subsequent media fearmongering is what really spurred the cultural shift towards helicopter parenting and a reduction in youthful independence in the US.
[1] http://www.theatlantic.com/magazine/archive/2014/04/hey-pare...
The comment I replied to said that "culture of walking and transit use" is key. And I'm arguing that it's not, using New York as an example.
As many have pointed out, the culture has simply changed. Crime is way down, but ironically people are more afraid to let their children travel unsupervised than when I was a kid.
As a side note, I did get lost on the train once (while in the care of a relative. She got off the train and forgot to take me with her.) I was asleep and woke up at a stop I didn't recognize. While I remember being a little apprehensive, I simply walked over to the woman in the token booth, explained I was lost and had gotten separated from my aunt. She let me inside the booth and called my mom, who came and picked me up. All in all, it wasn't a huge affair. I think if that happened today police and CPS will probably turn it into a major incident of possible child neglect.