Falcon 9 stages are stored on their sides unpressurized, see any of the numerous roll out videos, and factory images. There are launchers that require pressurization for handling (atlas 5?) but falcon is not one. Musk has mentioned this as a cost reduction and simplification withyou respect to encumbent providers, don't have a link unfortunately.
Bingo it's all about dynamic pressure: to be reusable the hull of the rocket has to land intact and not having undergone plastic deformation of any kind, so it's as close to "factory condition" as possible.
