Wow. I was just coming on here to ask the exact same question!
I heard a friend talking about her baby's birth in the caul and she said "but then it broke so he could come all the way out" and that made sense to me. But then our midwife friend who was listening said "well, it wouldn't HAVE to break" and that confused me. Because unless the placenta came out, too, it would have to break away from the placenta at some point...or be way too stretchy.
I think I've got it straight now thanks to Pam!