When I drain my little BX25D, the oil comes out ''plop,plop...' until the last pint is ready to drip out. unless I remove the fill cap then it flows.Same with many other engines, the crankcase vents are minimal.Although it's not entirely germane to the conversation, it's similar.
There are some vehicles where you have to pull the filter BEFORE you drain the oil. If you don't, it creates a vacuum and not all of the oil will drain out.
Our Caravan has such a motor,........................ and "yes" , I found out the "hard way" ......
So I can see where there might be situations (as @GeoHorn and @Hugo Habicht have pointed out) where the drain/refill systems create, or rely on, a vacuum of some sort.
