[erikpukinskis]

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.