A thought just occurred to me. Obviously, pulling out the crown of a watch for setting or winding opens the interior to the environment. Don't go diving with the crown unscrewed, that sort of thing.
Wouldn't that also open the case interior up for the "Ar" (nitrogen, actually) to leak out, and regular old, humid air enter the watch? Osmotic pressure alone would push the soggy DC air around here into the watch if that were the case (no pun intended)..