As was mentioned above, it's a lot scarier to think about sending your child outside to play all day when you don't know your own neighbors. My mom was fine with me riding my bike up the street as everyone knew each other. It's not that way any more.
This being said, I still think there's a way to get kids together to play and then let THEM do the game thinking-up rather than everything being little league, soccer etc - something structured. I think they need to make all the unused Borders stores into playgrounds for kids in the front and wine/Clive Owen porn for moms in the back.