I've got pretty average-sized hands and finger reach (which I know from piano lessons). With an iPhone 4 firmly gripped in what I consider a natural way, my thumb can reach comfortably to the top-right corner of the iPhone display and very little further.
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).
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).