Airplane Design Q&A

You are correct about maintenance being a big issue. But another big issue is that the airflow on the top of the wing is much more critical than the airflow on the bottom of the wing. Air on the top of the wing is moving faster and has an adverse pressure gradient (it wants to separate away from the wing). Air on the bottom of the wing moves slower and has a favorable pressure gradient. That's why missiles, engines, flap fairings, etc. etc. are located on the bottom of the wing. Those two jets you mentioned didn't have room under their wing for engines. (That's a big reason why bizjets rarely have wing-mounted engines. They want short gear so the door can double as a staircase.)