Wheel Sensors?

Recieved my Black 08 #4 Prius on Monday and purchased aftermarket rims the next day. I got stock size rims so I wouldn't have to buy new tires. While the rims were being installed the installer cracked the rear drivers side tire sensor. He said he replaced it but that I would have to go to the Toyota dealership to have the sensors reset. A little exclamation point(!) light was lit up in the dash but other than that there was no problem. Today I went to the Toyota dealership to have them reset the sensors and they told me it would be $95. Later on they told me that the sensor the tire shop had put in was not compatible to the toyota prius and that the sensor for the prius was $118. Picked up the car this afternoon and took the bill to the tire shop to reimburse me and gave them back the sensor that they installed. That's when they told me that they would only be reimbursing me for the price of the sensor. When I asked about the cost to reset all the sensors to get the light in the dash to go away they told me that when you buy rims on new cars with sensors that they have to be reset anyway. I walked out pissed off but without any knowledge to argue back with. Does anyone know if this is true? If this was the case, it would cost me $95 any time I took a wheel off or changed a flat tire. By the way, what exactly do the wheel sensors sense? Any help would be greatly appreciated.