I agree. It's definately not unheard of now. I have four kids....6, 9, 10 and 12 and they all are allowed outside for extended periods of time without supervision. I don't even know where they are half the time as they go from yard to yard, into the woods, in and out of people's houses. It can be hours and hours (and hours) before I see them again. Do I ever get uncomfortable with that? Sure. But they are kids and they need their freedom to play independently and just 'be kids'.
I do think this notion that "kids don't do that anymore" is a common misconception, and sometimes (not always) even an excuse for those who feel the need to defend their position to not let their kids roam freely.
My neighborhood is definitely one where kids play outside by themselves and where "be home by dark" is still heard. That's one of the reasons we moved here. It's a pretty generic suburban neighborhood, so I can't imagine it's all that out of the norm.
My almost-3 year old plays in our fenced in backyard by himself, and I'll stay in the kitchen where I can see (and hear!) him most of the time. I don't let him play outfront by himself yet, but just last week he played out front with the neighborhood kids for the first time without an adult - there were six kids randing from 3 to 13 out front, and I felt totally comfortable with his being out there. I didn't leave him alone long (maybe 10 minutes, if that) mostly because I didn't want the older kids to have to feel like unpaid babysitters.
If he isn't capable of being out front alone by the time he's 6 or 7, I will definitely be disappointed in myself.