I believe it can also vary for women depending on where they are in their monthly cycle. You never hear about that in erotica:
"Clearly she was due to start menstruating, because her panties were drenched" :D
It varies for me, like all the other comments above. I can also remember one or two occasions where it actually did run down my leg, but I am talking 2 or 3 incidents in 15 years. During prolonged foreplay, or if I am especially aroused that day, I can make my pants damp/wet, but it is usually a little spot. Can't say I have ever "soaked" my knickers. Erotica embellishes though. I mean, have you ever read an erotic book in which they describe the guys penis as anything less that "amazing, huge, massive, thick, perfect" These guys always have bigger than the national average of 5. something inches. Usually they are around 8 inches (from my recollection)
Erotica is fantasy, just as porn is fantasy for men (and women...not to generalise lol). It is designed to get as many readers as possible, aroused. It makes sense then that they try to exaggerate the hottest parts of sex...the wetness, the sizes, the orgasms, the moaning...etc to really paint a perfect, arousing fantasy in your mind. It wouldn't work so well if they described "normal" sex...
"He pulled down her panties, noticing she was still dry, he grabbed the lube"
Yeah...take it with a pinch of salt and just enjoy the fantasy I guess!