@range: ok.

This use case is based on single hand use, as mentioned previously, when you have your other hand preoccupied with holding an object, person, etc.

And, yes, there are ways to hold the device single handedly and still get access to the side button or whatnot, but that means you have to take it out with that sole purpose in the first place. By putting shutter\primary buttons near the 1/4 bottom of the screen, you can still possibly switch between different programs and maek use of them, single handedly.

Well, at least that was the aim anyway, if we want to have usability parity against most (90+%) other handheld device\phones.