But it does exist, even in the small sample that is Flyertalk there are reports of people getting upgrades at the window - including in this very thread. It would be simple for UA to win this argument in court, which as jsloan says, is why no class action lawyer would even look at your case. Just like people claiming PlusPoints are false advertising/impossible to use, I can assure you every day thousands of passengers successfully get CPUs at the window (and successfully use their PlusPoints).