Certainly not an uncommon event. I know in AZ, on the boys side, plenty of state league teams that are just as good, if not better than the ECNL/MLS teams. Even when poached by ECNL/MLS, those teams routinely replenish their teams. Given the population of CA, I would think this isn't an uncommon thing.
Letter league pay to play is squarely in the camp of those that can afford it and have college aspirations. Just the way it is. The MLS is looking to break that cycle, casting their nets wider and not having a college play focus. We will see if it lasts.