It would be interesting to know if this is caused by the sexual objectification of women. We live in a society that sees women as the 'sex class' therefore heterosexual women may be subconsciously affected by all the messages that say women=sex and their bodies reacting to that association? It would explain why men and lesbian women aren't like this to the same degree about men, because as the default human they aren't assumed to be equated with sex?
I'm married to a man which has been really my only major relationship so I haven't had a relationship with a woman. I don't think I'd declare I'm homosexual/bi/bi curious/pan because it is all a bit hypothetical. But I felt sexually attracted to women who I've felt emotionally connected to, and don't feel physically attracted to male strangers - I've never really got the "phwoar" thing people have about celebrities, random people etc. I'm more attracted to character, qualities than someone's physical gender/sex. Which may make me demisexual, or something else - I don't know all the terms people use. If I ever find myself single, I'll try and work it out.
So as I don't see myself as strictly heterosexual, I'm not surprised that other women may feel the same. But perhaps a bit of a leap to say that "no woman is totally straight" when it isn't clear that that is what the body signals picked up meant - especially as it doesn't tally with what women say they experience their sexuality as.
When I was young, my elder sister said she thought I might be a lesbian (which I unfortunately took in the same vein as her telling me she thought I was abnormal, and that may have been how she meant it) but now I wonder if assuming I was heterosexual was more about proving her wrong than being a reflection of my true feelings! Sisters eh? 
