Every week I see a good share of passengers with the same attitude. I just don't get it when somebody says "I have a full Y ticket" and thinks they're the least bit entitled to a J seat. If coach were oversold, I could understand. If as part of their frequent flyer program, Delta advertised that international upgrades would be offered to Platinums on full-Y tickets (not a bad idea), I could understand.
Now, on the other hand, when I took my job with the airline, it was specifically because part of the package was the space-available business class travel on the airline's network. So, yes, as an employee I am entitled to that seat if it otherwise would fly empty.
If getting a business class ticket for cheap is really that important to you, I suggest burning 180,000 miles more often or get a job with an airline. I turned down a $70,000 a year job out of college and took my $9-an-hour job specifically because I wanted to sit in business class more often.