Without knowing specifics, I can't tell, but in my reading experience it's not he audience, but the AUTHOR trying to do a little self-justification. For the longest time every bit of literature that had lesbians in it spent a huge amount of time either depicting them as deviants, or making a huge apologia for them.

Unless the fact that the woman is a lesbian is germane to the plot, I personally wouldn't ever focus on that. I think the way to go is to depict a lesbian as you would any other character. If their romance or lovemaking or relationship needs some description to move the plot forward, then you do that.

I get VERY tired of books with gay characters either explaining why they're really good people and not deviant pervs, or spending tons of time on the inner state of the gay character angsting about being gay when it's not germane to the plot.