The 4Runner tire pressure warning system uses pressure sensors in each tire which transmit to the vehicle via radio. [The senders are digitally coded, so that you don't pick up another vehicle's sensors. If you change wheels or sensors (in the valve stem, I think), the digital ID of the new sensor has to be "registered" with your vehicle.]
The system doesn't work by detecting the actual pressure value, it works by detecting a difference in pressure between one or more tires and the rest.
I don't believe that the system uses the rotation-difference method, although differences in tire size (and thus rotation difference) will mess up your Vehicle Skid Control (VSC) system.