In addition to all stated above-- or really just to amplify-- a single -J- seat on certain long-haul routes can be worth a good % of the price of an entire AONE. So, if the plane is heavily booked in J, we certainly have to understand the loss the carrier would be subjected to if they had no capacity control on their business cabin and had to give the last (or next to last, etc.) premium seat to a AONE customer rather than a paying full-fare J customer.