I was with you until you got to this
Originally Posted by hb1
The marginal benefit of charging $25 to fill the middle E+ seat with an upgrader is IMO outweighed by the benefit of keeping elites and full-fare pax happy.
I wouldn't not want UA to keep from getting $25 (or more) for that middle E+ seat.
But like you, I wouldn't want UA to just give it away either (if E- is still available).