I am pretty much like you, GirlinGray. Being bi isn't WHY I'm poly. I just happen to be both. My first step into poly was actually with a secondary male partner. Right now I am in a relationship with another woman, but that is just the way it happened.
I do know a lot of married bi women, though, that would not say they are poly but would still be open to dating/a romantic relationship with another woman. So by definition they could be considered polyamorous (capable of loving more than one), but they don't consider the love for a man and the love for a woman to be the same kind of love, so they don't feel a need to change their status from monogamous to something more encompassing.