Since Delta started the "L/U" policy, I have never failed to get an upgrade. Not once did I sit in coach. (This was at both PM and GM levels).

It is a boon to those who aren't flying at the lower fares.

As long as the rules are clear and adhered to, I can make an informed choice as to which airline gets my business. If I always flew on the lowest fare, I would probably use another airline.