Muddy, I would bet it something to do with all of the above. My 9 year old comes home with at least an hour and a half of homework plus 30 minutes of reading time. I don't have any console games in my house, but Big Al does have an outdated Gameboy. Many things compete for his "spare time."
With winter and shorter daylight periods, outside time is at a premium. Legality issues and insurance issues have caused most "games" that kids play to become organized. I live next to a state of the art multi use sports facility, yet the gates are locked when not in use. I'd think for the taxes we pay here in NY, we'd be able to budget some open field time.
Enrolling your kids in organized sports is expensive. It was $85 per kid for a spring baseball league. You get a t-shirt and a hat. And if, like in my case, you know a bit about baseball, you are encouraged to assistant coach. Three years I was the bench coach for the the Yankees, the Irondequoit Yankees that is, LOL. Add to that expense, a glove, bat, batting helmet, sliders and cup, socks, chest plate (Al pitches, so its a must), cleats, plus batting practice at the cages, and you're talking a significant chunk of change. In these times, not everyone will be able to afford it. There is the local Y, but that is pricey as well.
I agree, kids are not as active as they used to be. But it isn't just kids - its everyone! We ALL are getting lazier. This is why doing things like hunting, fishing, hiking, camping, whatever outdoor stuff you like is so important.