Well, straight people, by definition, would only be attracted to the "opposite" sex. A straight man might feel uncomfortable to find out that a woman he's been dating actually has a penis under her skirt, yes?
Bisexual men would be attracted to both genders, on opposite sides of the scale. They might not feel sexually interested in a person who seemed somewhere in between the 2 genders.
Some transpeople I know have given up on IDing someone by their genitalia. Gender is in the head. They might say, "I like femmes," or "I like butches," and not care whether the femme has a vagina, or the butch a penis.
Just random thoughts.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
There's no lying in polyamory!
I'm a 58 year old woman with 2 partners:
miss pixi, my live-in gf, 36 (together since Jan '09)
Ginger, bf, 61, married, lives nearby (together since Jan '12)