As a POS myself I think that WN policy is a very hit and miss thing. As you've seen on the Airline show, people will have been flying 20 times, and then get a ticketing agent who decides they might be too big.
Even if the airplane is half full, in some cases or even empty they're hitting you up for another seat. If their policy is that they're only doing this so that you won't infringe on other passengers, this doesn't wash. Seems like a way to make some more money on an empty seat.
I personally would probably just squeak by their test, but for this and other reasons I wouldn't book WN unless I was in dire need.
What's the #1 phrase issued by people on the Airline show:
"I'm suing Southwest".
Pretty funny. I'm really, really, really, really, really glad I don't fly WN. I've never seen more drunk, uncouth and outright dumb people in my life. Of course with editing, you might just be getting 100/th of 1 percent of the real people, so I shouldn't be too judgemental.