“I’m on a cross country flight. We are being diverted midway through to Denver. The reason? Some dude is sitting in the exit row who didn’t pay the $155 fee and he refuses to move back to his seat.”

There is a reason for that, though. Seat upgrades at the last minute introduce difficulties for gate agents. I don't work on that side of the airport but a friend explained it to me (i also fly standby and end up in good seats all the time, as well) When processing and pushing standby people, its easier to throw them in the available upgrades, rather than go through the list of passengers already booked to move them up. "hey, i have this exit row, you want it?" "no, my wife will still be in the back" then they have to go to the next highest tier person to offer them the same seat and so on. Then have to go to the standby list and move them into the most recently vacated seats. He was saying that its very annoying to have to move someone from x seat to y seat, then have to process the standby people, who are willing to take any seat. So why not skip that step and just fill the seats with people who will take any seat. It is frustrating as a paying passenger because if I chose standby, i'd usually just get the better seat.