I admit there is a market for small phones. Maybe, after Tim Cook era, Apple will smash big screen phones and pick up 3.5 again.The difference is that apple never made iPhones of that size. There is simply demand for a smaller iPhone regardless of what the actual screen size is. 4 inches just makes sense given it would be the most cost effective road if apple wanted it to be. Put an A8 + NFC chip in a 5S body, like the iPod touch 6.
However, everyone has relatively different life circle and social circle. This could lead to different survey result because of this. Those public surveys would have the same limit, even they have relatively huge survey target base.
Despite of this, I would say bigger phone is a new trend nowadays. Not only because those Chinese prefer bigger phone, but also bigger phone would let many users stop purchasing iPad or other tablet since the screen is large enough for many uses. My mom prefers big screen too. Single hand use is a sacrifice of course, but this is a trade off.