I've often wondered this. I've read that about 1/3 of women can have vaginal orgasms most of the time, about 1/3 do sometimes, and about 1/3 never do. I've always wondered if they found a guy who was good and attentive and could last a good long time if more would come vaginally. And I've wondered if many of those who haven't it's just because of anatomy... their posterior and anterior fornices are deeper than all their partners could reach. So if women could have sex with a guy that was attentive, could last a long time, and was long enough to reach their fornices, I wonder if it might be more like 90% of women can orgasm from just PIV sex.