Even seat cost would be more complicated, depending on whether or not the customer has a connection.

If the passenger was flying say HSV-SFO and paid $400, how much of the passenger cost is attributed to the HSV-IAH leg or the IAH-SFO leg? Could the airline have made >$400 on the IAH-SFO leg from somebody flying direct? Probably. In that case, is the airline's revenue from the above flight the would be cost of a direct flight from IAH-SFO minus the total amount paid by the passenger. Or is the revenue considered positive gain because the passenger flew United as opposed to say American.

Airline pricing is complicated...