I think it's safe to assume that they're abiding by the same state regs that apply to doctors' offices. Notice the wimpy nature of the doctors' complaints.
Massachusetts is the only state, as far as I know, where ultrasound exams must be "backed up" by a doctor. And even there, the doctor doesn't have to be in the same building. The exam can be sent via computer to a remote location and the doctor is obligated to review the film in something like 12-24 hours.
In an emergency (like a potential miscarriage) I assume that the staff is obligated to call an ambulance or recommend hospital treatment.
I wouldn't be surprised if there are doctors out there defending turf (it's so hard to be an obstetrician these days) however I don't dismiss their warning out of hand. Pregnant women can be stressed by a lot of things, I know I was. Worrying about extra tests and taking them is something I'm glad to have avoided.