I honestly find this EXTREMELY hard to believe, considering the NUMEROUS amounts of "non-revs" (used to be one) that fly. If profit margins were THAT tight, "non-revs" would not exist...
You do have a point but the economics of flight are almost as bizarre as the physics ;) On a more serious note, the biggest challenge of making money in the business is getting bums into every seat, because airline seats by their nature are the ultimate perishable commodity.