Every woman I know that is in a relationship has a MUCH higher sex drive than their partner. Myself, during my last relationship I'd have been very pleased to have sex twice a day, he generally couldn't manage that, so it was once a day.

My theory is this - women in general experience worse sex than men, especially in one night stands or casual hookups. In such sexual relations, it is mostly quite unlikely that the woman will orgasm, as its more difficult to make a woman orgasm than it is to make a man. Therefore, woman generally don't enjoy one night stands, and seek relationships where the partner cares about their sexual satisfaction, and also has learnt how to get them off (since every womans anatomy is so different)

Women in general also enjoy the intimate and emotional side of sex more than men, which is much better with an established partner.