I think different people do it for different reasons. I am sure there are people who are desperately trying to validate their own choices, or to come to terms with their own disappointing birth. I am also sure there are others out there like me who just love to hear birth stories! But I would never ask in that way. In fact I wouldn't ask anyone who I didn't know well. And then I would say something like "so tell me about the birth" or "were you happy with how the birth went?" or "was is a long labour?".