I am also an engineer, and I say that most of the speculation in this thread supporting the thesis that curved tubes are inferior is without basis. The mental model of tubes as a simply supported beam doesn't fly. I think the long practice of using curved tubes without any problem demonstrates that there are no significant differences between curved and straight tubes in a bicycle structure. Go do a survey of bike racks, and you'll see. Ductile metal tubes are made by repeated cold deformation processes, it doesn't hurt anything. Rolling or bending it any other way doesn't seem to hurt it either, that's not where you see failures