Proudelitist

That's both stupid and difficult to enforce. Once the booking is made and paid for, how would they know you ended up upgraded later?

What if it wasn't even a frequent flier upgrade or buy up, but a rare bit of luck...your seat is broken, Y is full, suddenly you are in F? Are you supposed to turn it down?

I had a boss that was just terrible. I had been a VERY frequent flier prior to going to that company, so I had tons and tons of miles and was still enjoying the benefits of high tier elite status, and getting auto upgrades on every flight we were taking. Not only that, I was skilled at booking the lowest fares. A colleague...let's call him "Jones"...and I had to fly somewhere for a meeting. I paid 200 something for my base fare, and Jones paid almost 300 for the same flight. I got upgraded to F. Boss hears about it and tries to dress me down for it..."You are not supposed to fly in First Class"...I told him I bought a coach ticket. He says "You are not supposed to fly First Class". I explained how FF programs work. I also explained that my upgrade, was..technically..up to the airline, not me. "You are not supposed to fly First Class. It doesn't look good to your peers".

Of course, he got fired months later for expense abuses.