What? Maybe I just didn't feel like typing an exhaustive list of everything I do on a phone. I certainly need to reach everywhere on the screen quite regularly. The URL bar and generic "back link" in most apps are at the top of the screen. And those are critical to app use.
You do make an interesting observation though. If there were literally no touch interaction points outside of my thumb arc, because the top and sides were 100% exclusive content-only, the screen could actually be much larger and still 1 hand operable. Assuming it wasn't too big to grip securely. But current iOS has me quite regularly touching all 4 corners of the screen.
Interesting. I guess web browsing is slightly easier one handed with a smaller screen since the url bar is at the top. The back link on Android phones is actually at the bottom and the fact that you can use swype keyboard, plus the fact that the screen size is bigger making key registration more accurate actually means I can use my Galaxy S4 for one handed texting (what I do 99% of the time) easier than any iPhone.
What people may not realize is that a Galaxy S4 with a 5" screen is less than 1/2" wider than the 4" iPhone (about the width of the end of your pinky), and considering you only need to reach that far when you're at the very other end of the keyboard, most of the time the extra stretching involved in texting is much less than that. That extra 0.4" or so gives you about 25% more screen real estate. Definitely worth it. Once I went to a 5" screen my old phone seemed like utter *****.
got tired of my wife with her 3GS always stealing my phone to play games on so I got her a Galaxy S3 for her birthday.
Personally I think 5" 1080p is the sweet spot where I can easily one hand text and it's the right resolution and PPI to play all full HD content natively.