In the simplest case, everything you learned in EE is correct. A potentiometer is a voltage divider and the circuit drawing looks like this:
In this case a significant amount of the voltage is dropped across R1 so the potentiometer does dissipate a sizable amount of energy.
However, having said all that, I seriously doubt if that many of today's devices use simple potentiometers. Even though my knowledge of electronics is a bit dated, I would assume that some form of gated device would chop the AC waveform limiting current flow by controlling effective voltage without having to dissipate power like a potentiometer would. Essentially, the gate chops the waveform so the circuit is "off" during the higher voltage portion of the sine wave; since the effective voltage is lower the device produces less heat. The "truncated" AC wave has and effective voltage determined by the RMS (root mean square) voltage and the power use (heating) can be calculated from the RMS voltage).
That's a lot more than you probably wanted to know, but it was fun dusting off my EE stuff again.