I do not expect I will be buying another iPhone ever again. The device is far too tiny...
Different strokes for different folks. I'm 53, have pretty poor eyesight (been wearing glasses since I was 10)... and actually prefer the 3.5" screen size that was on my old iPhone 3GS (or the LG Thrive I also had at the time) than the 4" display on my iPhone 5. I prefer not to have to use two hands to operate my phone, and with the 5 the top row is reachable but sometimes requires a bit of a stretch with my thumb (and I'm a 6-foot guy with normal hands). I really think those smaller screens were the best size for a phone. And, at least right now, I don't have any trouble reading stuff on that "too tiny" phone screen.
Now I also have an iPad Mini, which I use far more often for reading the web, playing games, and such - so the iPhone isn't my only mobile device. I understand that some people just want a single device, and there are compromises involved in making that choice. But those giant phones can't be used very well one-handed - that doesn't matter to everyone, but it does to me.