It's just one piece of bad manufacturing!
In many cases, people don't even see if the light is on or not.
In such cases you might as well save the battery!
I don't know how much the touch screen uses, but hope it uses very little, and turns off when not in use.
More than likely, the touch screen uses more power than the screen light, when setting it below 3.
Amazon knows they could have easily turned off the light. It would have made so many people worry less, in a society that has learned to preserve energy when they can.
Maybe in the US it's less of an issue, but generally in the rest of the world, you also turn off a light when you leave the room, or don't need it.
For many europeans (and asians, and perhaps other people in the rest of the world), leaving on a light, when leaving a room, is like leaving your car in a parkinglot, with the car keys on the door.
It just does not feel right.
Amazon does not seem to understand it, and despite the updates, hasn't yet addressed a 30 minutes programming error like this!