In a typical American suburban environment, "play outside" means play alone in the confines of the backyard, or be shuttled in cars by parents to "play dates", with most roads lacking even sidewalks.
Even then, I live in a high-density area with a park across the street and I'd be hesitant to let kids below ten at least go there unsupervised, if I had them. Whereas if I had a backyard I could tell them hey, go nuts, and peek out the window every fifteen minutes.
Of course I'm not defending streets without sidewalks. I'm defending the sort of place I grew up, which combines quarter-acre blocks and trees and parks with having shops and schools and libraries within walking distance.
I grew up in apartment blocks very similar to the image that was linked elsewhere in this thread: http://lh5.ggpht.com/-zHv1hczQcD4/UdgqTs1G3cI/AAAAAAAAqCI/le...
These were mid-rise buildings connecting together to form protective courtyards, filled with gathering places, playgrounds and mini-parks, inaccessible to cars, where 5-year olds could play, and 10 year olds had the whole city accessible to them thanks to good public transit.
>> I'm defending the sort of place I grew up, which combines quarter-acre blocks and trees and parks with having shops and schools and libraries within walking distance.
That sounds like a pretty rare place though. Walking distance to schools and libraries tells me either pedestrian-friendly high density, or a very small town with not many job options. If it's neither, I'd love to check it out. Where was that, if you don't mind?