Default 2 day battery life

A friend of mine got a Xperia Z1 and told me he got almost 3 days with one charge. I didn't believe him at once but then I looked at his battery history. And he really had 2 days and 13 hours. I was amazed! I know Z1 has a HUGE battery but 2 days of huge battery?? It seems too good to be true.
Can anyone maybe explain how come he can get 2 days with 70% screen brightness and I can't get 1 day with 40% screen brightness on my One X?

PLUS, http://developer.sonymobile.com/2013...peria-z-ultra/

Why don't all smartphones with huge screens get that amount of battery life?