My husband is an OB resident. All of his months but two are at his home public institution, but those two months at a private hospital really opened his eyes. He says the women at his hospital recive less interventions *because* it is the residents delivering them. My husband works night shifts, he is not on call nights. If you are his patient in labor, their is no incentive for him to dose you with Pit or call a premature c-section because he is not going to sleep or going home, no matter when you deliver! Public Hospitals are a 24 hour a day operation, while many private hospitals are competing with the doctors outside lives, clinics, and schedules. If you do not give birth during my hubbies shift, you will give birth on the next one. He still gets the same crappy paycheck if he attends one birth a night or 25. He gets no higher compensation for a surgical birth than he does a vaginal one. Money and desire to leave the hospital do not cloud his judgement of how to handle patient situations. So, he does the best he can for his patients for the short time he has them. Residents don't suffer from "Failure to wait" syndrome as much as docs in private hospitals do, because it really does not impact them personally at all.
Also the liablity issue, private docs do more montioring and interventions to cover their butts. If it looks like they "did more" it is better for them in a malpractice case than if it looks like they did too little. Docs in public hospitals have less to lose. The hospital pays their insurance premiums, and the hospital is ultimately responsible for all that happens with residents. State hospitals are offered more protection under the law.
As for more interventions equalling more money for docs, fraid not. You get one flat fee for the whole bundle of prenatal care and birth (slightly higher for a c-section). So essentially if a woman comes to the hospital and has the baby in one push, or has a three day ordeal with Pit, forceps, a big tear and repair the doc is usually getting the same preagreed amount form the insurance company.
Oh- and as for the question about being able to deny residents from attending your care in a public hospital. I know in DH's hospital you can say no students observing, but you cannot say no residents, since they are the doctors that primarily staff the hospital. You can refuse treatment form any particular resident, nurse, etc. but not "Residents" as a group. But that goes for both privately and publicly insured patients. (But, lower level resident usually see public patients and they usually give the more experienced residents private patients- shitty, I know).
It is actually pretty amazing how progressive most of the residents DH works with are. They think it is awesome that we are having a homebirth this go-round. All of the female residents use the hospital midwife service when they are having their own babies, and forego most prenatal testing. Dare I say there could be hope yet?
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... and in my area, their episiotomy rate is the lowest because they did some study which found it was unnecessary and not cost effective 
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