How is this any different than listening to Pandora all day at work? Or watching a live news video feed all day? Those things are totally acceptable, NORMAL usage patterns.
The "abusers" are doing things like using the iPhone to tether their laptop and torrent stuff. A difference in magnitude of bandwidth usage.
Because he purposely wasting data just to abuse The unlimited aspect. Even of its the same amount of database running it during the day it was a waste because he wasnt actually using it.