More attractive females tend to have fewer sexual partners actually. I think it's because less attractive ones think that they can hook a more attractive man by giving him good sex. In reality, they just end up getting hurt. The real long term damage is in the fact that they can easily sleep with relatively far more attractive men, and this increases their standards for what they think they can get for relationships. These high expectations are either lowered, when reality hits really harshly, or they aren't, and you get a foreveralone catlady type.
The power of female choice: Fat chicks get laid more
Of course, as with every other sociological trend, by definition, exceptions most certainly exist.