GPS / phone network tracking probably has lower precision than short-range bluetooth. Bluetooth receivers can be present even in places without network reception or GPS, and receive signal passively and without a trace.
I guess I'm not clear to that extent the NSA hacks people phones. I would imagine for most users they would have good access to our GPS data, e.g. via Google Maps?
Edit: I'm assuming that GPS level precision is sufficient to start the dystopia
