The only way it makes sense to me is this: Apple designed the iPhone to be a pocketable one-handed companion device to a real computer. People started using t

The only way it makes sense to me is this: Apple designed the iPhone to be a pocketable one-handed companion device to a real computer. People started using them as their only computer. The changed the design parameters enough that it made sense to offer a less pocketable device with a much larger screen. The thesis is: maybe that market can be segmented even further, by adding an even less pocketable segment with even more screen space.