Those upgrade lists at the gate are a bit deceptive because they are actually listing all the UA elites on the flight (excluding those who have already received their confirmed upgrade) since all elites are eligible, but in reality only a handful of Global Services and 1Ks make it into the front cabin. So far I am 100% on these upgrades since they've started, always being confirmed within a day or two of my 72-hour upgrade window. I do think that this new practice at UA, while great for top tier elites, is pretty much eliminating upgrades for PremEx and Premier members on all but marginal or off peak flights.

Of course, UA can afford this because it seldom sells F domestically, filling it with either premium fare payers connecting onto/from international flights or elites who are upgrading. AC still sells higher fares in coach (permitting at purchase Latitude upgrading by elites) and J, so it would lose too much money copying UA and CO and other US carriers doing this. American carriers also have many more flights to amortize these costs against than AC, another factor as to why AC is more restrictive in upgrading opportunities for those not paying full Y type fares.