Originally Posted by radonc1

Many have said this lots of times. If you want assurance of a first class seat, either buy an F sear or an upgradeable Y seat. Have you tried to book a B or M upgrade seat to see if they are available? If they are not, then CO has a high expectation of being able to sell those seats as F seats. This happens to me often, especially on the LAX-CLE red-eye where B seats book into the back of the bus. (They usually still get the EUA eventually, but not at 6,5 or 3 days before the flight).
I have seen many a flight from CLE-LAS have 14 open seats 1 week out to 7 seats 4 days out to 1 seat 2 days out and sold out at flight time. It is CO's job to make money on these seats, and as far as I am concerned, as long as they don't sell them for less than what I would have paid when I booked the reservation, I am satisfied with the system.

Upgrades are bonuses for loyalty, not rights.