I have yet to see any airline restrict carry one baggage that is obviously over sized and require it to be checked.
I saw it this past Sunday while waiting to take off for Buffalo...on US Airways.
The flight attendant saw the size of a woman’s ‘carry on’ and told her she’d need to check the bag immediately because it was over sized. I was shocked. That never happens. The woman started to complain but the flight attendant simply told her she was free to take another flight because that bag was not going into an overhead compartment.
Same thing happened to me on a US Airways flight - on a flight that was about 25% full with plenty of overhead space.
The flight attendant was rude as hell.
I took her up on her suggestion that I use another airline on the spot and walked back to the ticket counter of another airline.
She made it very plain to me that neither she nor any other US Airways employee could care less whether I flew with them or not.
I have absolutely no doubt that she was being 100% candid with me.
That was 4 years and about $250,000 + in passenger revenues ago.
I tend to fly a lot but I have never had this problem with any other airline.
Behold, the union mentality.