Aircraft routing is a complex maneuver. Most International stations for many airlines only provide unscheduled maintenance, or light maintenance, during the turn. By routing a heavy jet from say: NRT-SFO-DEN-ORD-IAD-LHR (using UAL as an example) you can complete the required maintenance AND provide a premium seat domestically. Of course the cost of multiple cycles and short legs would be a concern - but like you say, the bottom line would tell the tale.