From my experience it can vary quite a lot within individual women (different times, moods, etc.) let alone between women, though as we all get older there is a tendency for everyone to dry up a little. In terms of stories, it is like easing into latex clothing or buckling up a collar, it is not actually like that in real life, but as it says on the top of this website, this is a location for fantasy and a story in which it takes the Dom half-an-hour to get into their latex catsuit and gets talc everywhere and then another ten minutes to get the tongue in the right place on their sub's collar and their sub is bone dry and not at all excited may be realistic, but not too much fun to read. Women getting wet is a shorthand to show what is going on. I must say I have never read a story in which the man has pre-cum appearing, despite being pretty common.