Regression to the mean suggests stabilization or increase would be more likely than this large decrease. Maybe someday we'll have some certainty on why it's happening. The whole lead-reduction/crime-reduction thing seems really strong, but not definite. The "more porn, less rape" theory also seems to have some support although not as much. "More abortion, less crime" is also interesting and the least supported in my nonexpert opinion (but can be tested overseas).
Anyway, it's nice to have some good domestic news along with the good news from the Arab world.
A tangent: I recently watched Predator 2 after being told it was good (my review: meh). Filmed in 1990 and set in 1997, it took the then-upward crime trajectory and sent it forward to an ungovernable future. Interestingly bad prediction.