Comment by navitronic

The 5's size was to maintain the 326ppi of the display and ensure a smooth transition for developers. A 3.5 and a 5 inch screen would have made app developers have to create 2 separate layouts, whereas this approach means that developers 2 similar layouts for 4-class phones (3:2) and 5-class phones (16:9), which should ideally mean less work for the developers