I'm not sure if they install the hardware sensors regardless & only control access via software, though, but I'd be curious about this for sure. Anyone know?
IIRC, when the Auto-Pilot hardware/option was originally released the "Tech Package" was a pre-req to buying the "Auto-Pilot" option.
For the autopilot features, the difference was only software. Even before the Autopilot option was first available to order in October 2014, cars were being silently shipped with Autopilot-ready hardware for several months. For those cars, it's possible to call up Tesla with a credit card and enable the feature over the phone.
These were moved to the Premium Interior and Lighting Package ($3000).