Re UA100/101
It's best not to read too much into the fact that the premium cabin is often full on US carriers. Frequent fliers get a bunch of free upgrade certificates, so they get to travel in Business even if they've bought an Economy ticket. This is particularly the case for US domestic flights ( where the premium cabins are always full in my experience, generally due to upgrades), but it also applies to transatlantics, where UA Mileage Plus members can use Global Premier Upgrades (GPUs) or Systemwide Upgrades (SWUs).
So a full J cabin on our UA (or indeed AA etc) services isn't necessarily an indication of good yields.
This would also explain why you've noticed a lot of Americans in the J cabin - they're the ones most likely to be using upgrade certificates.
Last edited by BasilBush; 13th Jul 2013 at 06:05.