I've never been a normal woman, so I've never routinely sucked in the gut. I only do that when I'm looking in the mirror or posing for a picture.
But I think most women do...in fact I'm pretty sure I remember my mom instructing me to do so. And my flute teacher used to compliment my breathing because I wasn't afraid to stick the belly out when I breathed. She had to break most of her students of lifting their shoulders.