I don't know how exact Disney's abilities are. They're using RFID triangulation, I believe. They have no purpose to track you down to within feet.
They want to know if you're on a certain ride vehicle, so that the photo links properly to your account, and that can be done with one directional scanner. They will someday want to know if you're near Mouse Gears, so they can entice you to go in and buy something, but that can be done with one or two scanners and only needs to locate you to within a moderately large area.
But it's important for them to be able to track the EXACT location, speed and direction of parade floats for safety and proper spacing/timing.