The thing to remember is that you're referring to a screen in an actual dashboard, one that must be appropriately bright to various day/night conditions. It's probably more important than the knob that adjusts the dashboard brightness in your car, probably especially because your dash isn't illumunated during the day unless it has some active displays.
Granted, but you'd think a dial or knob would be more efficient than six discrete buttons. Heck, why not two buttons?