Fair enough. On the other hand, the percentage price increase it's worth paying for that, is perhaps on the order of the probability that your phone would otherwise die from that cause rather than some other. I suspect actually making a phone waterproof to a hundred feet (as opposed to just moderately water resistant) would cost more than it's worth paying.

Not necessarily. I would pay somewhat more, simply for having more faith in the device. After all, a smartphone is the piece of electronics I use more often than any other throughout the day, and having one I enjoy using is worth it. Knowing that it's well engineered and won't let me down soon as I sit down and it slips out of my pants pocket onto the floor, or that my kid can't drown it, or my wife can't run over it with a car when I drop it in the driveway is a good feeling I'm willing to pay some amount of money for.