I think there is also a certain logic to the 'easiest-path' idea: it is much easier for the average evil male character to get what he wants through physical intimidation or violence, and much easier for the average evil female character to get what she wants through sexual manipulation.

I think the problem comes in when sexual manipulation is presented as the only option for evil women, as is suggested by the prevalence of the sexy 'bad girl' archetype. I can see it being a useful tool in any bad girl's arsenal, but it's not the be-all and end-all that one-trick ponies like Saffron present.

The 'evil power as multiple orgasms' trope takes it another step further. I think it would be hilarious to see it applied to a male character.