I'd compare NYC to Scarsdale. NY is losing a ton of teachers to the burbs, where salaries are higher and the risk of physical injury is less. Conversely, and oddly, NYC is gaining teachers from places like Georgia and Texas, where the salaries are low...
Well, Georgia doesn't have "low" salaries. Maybe lower than NY, but most are lower than NY. Also, when they get there and find the cost of living and the physical dangers I'd bet they'd reconsider.