McTimson: a philosophically interesting question. I've still got rear brakes...
Martin: I agree, it's probably more the lack of use than the light braking. Come to think of it, having spent the winter in the salt air of the east coast must have been extra hard on them. I had to oil my bike chain on the beater bike about twice a month all winter to keep it from rusting solid.
I'm a slow learner Frank. Seems it has to cost me money before I learn my lesson
But after I replace/machine these rotors & change the pads, I will try WD-40 if I know I won't be driving for a while. Of course, smooth wheel covers complicates things a bit...