This simple illustration highlights the areas iPhone users (A) naturally reach across their screens, (B) stretch to reach across their screens, and (C) stretch so far as to cause discomfort in their thumbs to tap or swipe. All things considered, your accuracy tapping in the orange or red is lesser than in the range of green.
Good thing the iPhones 6 feature Reachability. It seems like a half-baked solution at a glance, but in practice I have heard that it works for some. I think the verdict is still out on whether users will adopt Reachability on a wide scale, because we have not had this problem before. And who knows what a better solution looks like? Designers haven’t encountered this problem until now, so revealed solutions are few at the moment.
They that like elegant solutions think it’s about the most unpleasant solution Apple has created in recent memory, but what would an “elegant” solution look like? ∞