The main reason I figured the temperature is self regulating is that the fuser is one of those parts that are different on a 120 volt unit or a 240 volt unit. It probably just kicks on with a relay.

I could be wrong, but I doubt they could get precise enough temperature control out of one of those little bimetal jobs to assure consistent print quality.

Of ocurs eI could be wrong, but there is still usually a different part for 24 volt operation, whereas most modern power supplies switch automatically.. Some don't even need to switch, they just have good enough regulation to run fine anywhere from 50 - 250 VAC.