Tim, thanks for bringing this point up. I have often wondered myself...its one of those things you always seem to hear about and read about, but I've NEVER talked to anyone who has experienced it with ball pythons.
I've heard of a healthy animal that laid a clutch of eggs and had a large or hard egg get caught in the oviduct and had to be aspirated to help remove it, but I do not believe it was due to the female being underweight or young... just happened.