It probably doesn't demand too much of the battery, but any reason the side view mirror heating has to be linked to the rear window defrosters? I don't think there is a separate button to heat the side view mirrors. Many of us don't need to melt ice off the side view mirrors in the winter, and I don't recall having much fogging with the side view mirrors. Rear window fogging, however, is something most of us will have to deal with even without ice/snow.
Well, the big picture, ie, the insurance companies have decided you need to see out your side windows more then your rear window, and if you refuse their advice will have a say in your hospital stay. But who says new tyres go on the rear, not the insurance companies, the resellers...it's just money honey?