The author states that the iPhone screen is perfectly sized to allow your thumb to reach the opposite edge. You seem to be agreeing with him.
I think you got his argument backwards.
I think you got his argument backwards.
I could probably extend well past the edges of the Android phone, as well. So I don't think that "average thumb length" had anything to do with the size of the iPhone screen.
So, while I think the diagram is exaggerated, the writer does have a point. My guess is that the 3.5" screen works very well a very large percentage of adult hands (say 75%) and acceptably for, say, 95%. I think a 4" display would probably pull things out of the bell curve. I suspect given that Apple probably made a LOT of prototypes that the iPhone's screen size was determined empirically.
To me, the iPhone4 feels almost exactly right in terms of width (I think it could be up to half as thick without feeling flimsy).