Pretty much this. Except the lawyers also win. The lawyers always win.

Skimming the complaint though it's possible that he might have a case. The issue is not that FF benefits got cut, but that they got cut at such short notice that people who had spent 2011 directing their flying to United on the assumption of getting certain benefits in 2012 found themselves not getting those benefits in 2012. I, for instance, qualified for Gold under the assumption I'd get a 100% mileage bonus, instead I'm getting a 50% mileage bonus, which assuming my flying remains constant means something like 25,000 miles I'm missing out on. And this sucks.

It may come down to precisely what United marketing did actually say. If you claim "If you fly 50,000 miles we'll give you a pony" then is a bunch of fine print saying "Oh btw we reserve the right to change our mind about the pony thing at any given time" enough to get you out of that legal obligation? Ethically it most certainly isn't... legally is another question.