Well, the rear window defrost button was on the dash & the mirror defrost was on the console. It makes sense to me that the rear window defrost wouldn't be illuminated as bright since it would be "in your face". IIRC, it's illumination should change with your dash light intensity (control at your left knee) while the mirror switch should not.

BTW, I've left my mirror defrost on for days at a time too (just because "out of sight - out of mind). I'd probably move mine to the dash but I'm not through procrastinating yet.