yea, they're supposedly getting it from porn, and such imagery...also as they said on the show (not direct quote) "from the time of sex and the city, when Brazilians and waxing became the in thing, women can see what's actually down there"
also they were never made aware of what's "normal" from the start. in biology texts fanny flaps are said to have a range of, from 2 -10 cm.
basically they never knew what was down there!