Seat Costs
Cannot help you with your question but I can muddy the water a bit more for you. In general airlines operate on the ASK that is the actual seat cost per Kilometre. I have no idea on any US carriers but would be very interested.
Easyjet UK operates on a 4.5 pence per ASK
BA operates on 13 pence (LGW) and 15 pence (LHR). From those two alone you can see one reason for Easy success. I should imagine that UA and AA would be on the dollar equivalent to BA, may be more.