I think it depends on the individual.
Zero bedroom experience, so take what I say with a grain of salt, but ...
I do not believe that most women vociferously moan as a natural reflex. I think that a few women might, but that for most women this is something they learn from somewhere outside themselves, be it books or films or whatever. I think the nasal moan (i.e. say "mmmmmmnh" as if you're talking in your sleep and it sounds just like a pleasure-moan) is much more common in real life than the one you often see in porn videos which is the expiration moan (i.e. say "OOOHっ! OOOHっ!" like a female porn star moaning). The nasal moan requires a lot less air to generate, and that makes it a better candidate during sex than the expiratory one. I mean, since sex can be a pretty exhaustive exercise, I'd think the woman's body would subconsciously shift her into whichever gear is most economic for her. Less oxygen to the voicebox and more oxygen to the thighs!