I've seen you say that before, but I think things have changed. MaryJanice Davidson's series, starting with Undead and Unwed, are unabashedly centered on romance, and the protagonist of all eleven books is Betsy Taylor, Vampire Queen. It's one of the top-selling series, and no one ever argues that it isn't "really" PNR. There are others that I would probably shelve with fantasy but get shelved with romance, like Marjorie Liu's Hunter Kiss series. So I don't think that criterion is withstanding erosion.
I tend to prefer "descriptive" definitions over prescriptive ones, and I saw a while ago that a PNR blog held a poll for favorite PNR heroine. Mercy Thompson won. She would probably be one of the top choices in a UF poll, too.
But enough of this urban fantasy hijack! The OP told us all to go to Hell.
Thank you! :)

