you are correct, the political climate and malpractice ins. situation does affect whether an OB would back up a midwife or not. I still maintain that it _does_ happen, and quite regularly. sometimes out in the open, sometimes not.
there is a birthing center in taos NM w/ at least 2 OBs on staff, a husband and a wife team that I know of. the birth center is run by a CPM who also provides a reputable correspondance midwifery program, and the center is mainly staffed by midwives. those Drs. back the midwives up. and they do it openly. it does happen in some states, albeit only openly in those such as TN and NM where midwives and supporters have worked hard to open up the option of midwifery care for women.
also, I maintain that a UC birth is a different kind of bird than a midwife attended birth. both are healthy valid options that I firmly believe should be available for women and their partners, but they aren't exactly the same.