I wouldn't see how you're hijacking the thread, since it's title is, after all, Diesel fuel evaporation.
You're right about liquids vaporizing all the time as a function of temperature. Obviously that is the case or we wouldn't be able to smell diesel at normal temps and pressures for humans. Not that the lack of odor proves something is NOT evaporating, but the presence of an odor, I think, proves that it is.
But there is something special about diesel and 140F. I can't find anything to support this, but, from fuel hauling days, we were required to do vapor recovery when filling gasoline tanks, but not when filling diesel tanks. The air in a diesel tank was considered to be 'air' and not vaporized diesel. I wouldn't want to make a habit of breathing it regularly, but it must have been considered non-flammable and non-polluting or the EPA and OSHA would have been all over it.