About .5" diagonally. Compare the two devices next to each other to see the real difference. Is usable display space is not an issue, no harm no foul.
That said, seems silly both being the same size, yet far less useable display on the One.
This is correct. I used both devices and the One's screen starts off .3" smaller and gets smaller in various apps that have the dreaded menu bar. It's most notable on popular apps like Facebook and Angry Birds. Supposedly, it is being address in the 4.2.2 update but when that update is coming to US carriers is anyone's guess.