I'm not at all sure that's true. UA flies a mix of aircraft on that route, including 752s. With 24 F seats on the latter, even a 2P has a decent chance of getting the upgrade. I know that as a 2P in the past (to which I shall return in 2012, alas), I got upgraded on the 752 at least 50% of the time on flights between hubs and non-hubs. ("The Hub" isn't one as far as UA is concerned.)