Their physiology is the same. Affectionate and sexual attraction (marital, platonic, etc) are all different. People's physiological "response" to people they are physically (not affectionately) sexually attracted to other people.
I'm talking about physical attraction not affection. John and Sandy both have physiological responses to other people as sexual and evolutionary human beings. That's their hardwire.
Regardless of who is more affectionate than another, they are "programed" the same: with the physiological response (erection and all that) to whom they are attracted. We're not attracted "like that" to those we are affectionate with (two girl friends, two men hug each other, say outside the States are still gay, straight, bi regardless of how much they snuggle together).
Sexuality (in regards to heterosexual/homosexual/bisexual/etc) is not speaking of affection and how women are more affectionate than men. It's specifically about one's physiological sexual response to men, women, or both. It starts to be pronounced in puberty and solidified when we mature as adults. People know they are straight, gay, bisexual before they are sexually and/or affectionate with anyone.
So, heterosexuals, homosexuals, bisexuals, et cetera cannot change their born evolutionary response to the people they are attracted (not affectionate) with. Affectionate isn't sexual attraction. Platonic relationships aren't based on sexual attraction either.
The reason two women can cuddle and be affectionate with each other and still be straight is they know for themselves their inherent, physiological, and psychological attraction are geared towards men regardless what they do together.