He might be one-armed, poor guy, while the vast majority of us humans have 2 arms. We've learned to involve both in just about everything we want to do (which is probably why we have 2). Apple comes along and spins 3.5" as the "perfect" size and rationalizes that- in part- with the one-handed use argument (which, of course, doesn't carry over to the marketing spin in selling iPads or iPad Minis) and "we" swallow that like candy.
Then Apple launches the 4" screen as the new "perfect" size and we swallow that like candy too, even if before hand "we" spun "they would never", "fragmentation", "abomination" and all such typical stuff.
Soon Apple will roll out the 4.7" and maybe the 5+ inch as the newest "perfect". And if the one-handed use part of the spin to rationalize that perfection will no longer apply, they'll just drop that bullet from the spin. Like all such spin, such bullets are only important when they support some differentiation thrust. In this case, Apple wanted to spin why smaller screens were better than bigger screens and that was one such point. So naturally, "we" run with it and argue it to no end- even make up relatively odd scenarios where it applies- right up until Apple drops that punch or spins something else and then "we" will go right with them.
I use both hands on an Apple keyboard to type this response. I use one hand on the keyboard and one on a mouse to review it. 2 hands on an iPad mini works just fine
even when on a train (and all such rationalized scenarios). The one-handed argument will just end as soon as Apple rolls out a phone that doesn't support it and they drop it from their spin. And then the crowd will flip with Apple and "shut up and take my money", "how did we ever get buy with those small screens" etc will chorus will rain upon us.
And almost no one will have to buy new pants with huge pockets.