I dont agree with you on this cause whenever we drive, inline with viewing the front upcomming traffic we also keep a vigil on our rear following traffic whenever we overtake,suddenly brake in emergencies or any other situations. through our right and left ORVMs and also the cabin RVM(mostly among the 3 VMs).For the view through cabin RVM the rear windshield glass has to be clear of water film(rain or other source) and dirt.