I think it just has to do with the different areas and neighborhoods people live in. I know what to expect from my neighbors. We are friends, we BBQ together, our children play together, and I would no more let harm befall my neighbor's wife than my own. The same would go for my neighbor's widow, or his daughter. If a case goes to court, then guess who will be on my jury. People who feel the same.
If I lived on Long Island in New York, I might just let my neighbor die and read about it in the paper in two days though. I understand that is the proper way to behave there. That's why many people in the South scoff at moving to other areas. We still have communities, and we know and like who lives around us. It's not about playing policeman. It's about behaving like a man. You do not let harm come to your friend's wife. Your results may vary.
Oooops, I changed the scenerio didn't I? All my neighbors are married or widowed, so it's understandable........ The same applies to a single woman who is a neighbor, unless she is recently arrived from New York and has an arrogant attitude towards Southern virtues.