I believe with bigger screens came higher expectations from consumers regarding resolution, since the boom of the hd ready and full hd TVs, and the market reacted accordingly and expected more, hence higher resolution devices. Manufacturers simply could've not bothered to update the resolutions at all on these bigger screened devices and kept them to a 720p standard or less, however they didn't. Sure innovation does play a part, as you said, but I don't see a single manufacturer of mobile devices stick to a resolution and call it a day, resolutions are increasing across the board, both in low and end end devices, globally. If we consumers didn't want higher resolutions, the appeal would have plateaued by now. By all means manufacturers can spend the budget in increasing screen quality at the expense of res, but that doesn't sell devices, including consoles and pc's, buzzwords to do with ever increasing resolutions do, imho. Gaf loves its 4K TVs, they once loved 1080p TVs. We even see that in the iPhone 6 keynote, with phil Schiller extolling the virtues of the bigger higher resolution screens by using the benefits to sell to consumers. The reason why iPhone 6 sold so much was in part due to the screen size, yes of course, but that went in hand in hand with the res, they delivered to their consumers what there competitors were providing. The 6s sold less, Apple has had recently a quarter or two where they shipped/sold fewer iPhones overall, despite the new hardware.