To an extent I agree, remarks such as SFU made be made against your booking but there is still an expectation that you should be suitably dressed for the cabin to which they intend UG you to. My experience is largely restricted to LHR - one of the hardest stations to score an UG from on non-QF metal and, more often than not, it happens at the gate (ie when they know there are no more BA Silvers or Golds to come before you).

I'm still curious about the earlier post mentioning UGs on LA: I've found them to be one of the meanest OW carriers - even for paid premium pax - along with IB.

On QF I only think I've scored an UG once, on a very short domestic flight, and that was by way of apology for some minor misdemeanour (which was graciously accepted).

I have found AA and CX to be the most generous of all; in the case of the former a dubious benefit but nonetheless an improvement over the next cabin down.