I had to laugh at this :)

He could be running long term processes in the background. You don't know :3

shrug. That's my usage pattern. I find it hard to imagine having the screen on for more than that on an average day, even if the phone is in active use more than that (e.g. when listening to podcasts, or taking a GPS trace during a workout). And of course there's the passive use of just having it constantly syncing. With previous Nexus devices just the passive background noise of Android was often enough to use up the battery in a day.