I had a shot of pitocin via drip line after delivery, as a treatment for post-partum hemorrhage that I was actually having. I also had uterine massage, and they offered me the baby so I could get started breastfeeding, but I wasn't really safe to hold him. I only had the IV for a little while - I think we were done with it before we moved to the post-partum floor - but I was in awful shape after delivery, and the time it took to, say, get me stitched up and feeling well enough to hold the baby was a definite delay in initiation of breastfeeding. (That wasn't caused my pitocin though. Baby was OP, I pushed for five and a half hours, and then I tore. It sucked.)
Research has indicated that active management of the third stage of labor, including administration of pitocin, reduces the risk of post partum hemorrhage by 68%, compared to expectant management, which involves only nipple stimulation and waiting. (http://www.aafp.org/afp/2007/0315/p875.html) I know that breast feeding can help prevent post-partum hemorrhage, but I don't know that it's the best way, and it's certainly not the only way.
There are risk factors of PPH besides managed labor. Prolonged labor is a risk factor, and so is precipitous labor - in both cases, muscle fatigue can lead to an atonic uterus, in which it's very difficult for the muscles to contract strongly enough to prevent hemorrhage. The link above also notes that many cases of post-partum hemorrhage arise even when there are no risk factors, so professionals providing care at birth should be prepared to deal with a hemorrhage in all cases.
I have never heard of a case like Kitteh describes, where pitocin-induced contractions allow the uterus to contract without expelling the placenta. Physically, there's only so small the uterus can get with a placenta still inside it.
The incident you describe with the nurse strikes me as a case of really bad nursing, and concerning for that hospital - A well-placed IV should not fall out, and her outburst strikes me as irrelevant to the situation. Sometimes there are bad nurses, and sometimes good nurses have bad days, but just ignoring a dislodged IV is not okay, nor is yelling at a patient who brings something like that to your attention.