A really good article from Grantland on the decline of NYC's high school basketball. A lot of really jarring numbers to support the claim. And a lot of great anectodal theories in support of why.
I particularly like the plain and simple theory that it's related to football. That the areas produce the best football prospects produce the best basketball prospects. It seems counterintuitive because of the specializing of a lot of the top athletes, but the fact is that football drives not only extra funding for facilities, but a culture of working out, and particularly weight training, that just isn't seen in cultures that don't embrace football on that level. Football is on the cutting edge of weight training.
Also, I remember meeting Tom Konchalski, a NY basketball historian interviewed in here, at an invite camp the summer between my junior and senior year of HS, and being blown away by the fact that he knew all this shit about me. He knew me as a basketball player, which was surprising enough, but also knew my GPA, that I was taking AP HS classes. It was a little creepy, because this was like 94, so it predated the world of recruiting as we know it now.