Actually, many do. They mention 4.7 typically, not 10. Make a 4 and 4.7, simple, you take your choice. One size doesn't fit all, as the market has shown.
if its just a phone then i guess one screen size should fit all. But phones were only phones pre-iPhone era. After it things changed. Its now a device that people do a lot of good stuff on. My primary email device is iPhone, GPS navigator, Primary (and only) camera is iPhone....and there's tonnes and tonnes of stuff can be done on it and people do.
So,
That leads us to one conclusion. The way one computer screen-size wont fit for all, Music pros need as large as 42-48 inches and often multiple monitors, cash counter would probably need just 10inches. Similarly, phones need different sizes. i would love to do some basic spreadsheet stuff on the go. some basic annotation of PDF and images. I see a lot of people watch videos/movies to kill couple of hours they have traveling back to home after work and so they don't mind carrying a phone that's bigger, bit uncomfortable cos benefits a lot more than the trouble.
For me, 4.5-4.7 inches will be great.