I'm guessing there is a sweet spot in the south when it comes to meat chickens. I've read they don't tolerate the heat well. This winter has been RIDICULOUSLY cold though. And I think southern chickens are wusses too. The days that we had 20F with snow/sleet on the ground, the chickens wouldn't even come out of the coop, lol.

It's whatever they are acclimated to and, it could have something to do with owners as well.....I've noticed that people who never acclimatize themselves to the seasons and stay indoors a lot for winter months with the heat on 80* will also think their dogs will get cold when left outside to live and will bring them indoors so they won't "get cold". When they do that, they render the dogs as helpless against the cold weather as they are, so it's all self-inflicted.
I see dogs tied to a box out in -20F, no bedding in their dog boxes and they are just sitting next to the box like it's a sunny day. My dog has a very warm, deeply bedded dog house with hay bales stacked all around it and a flap that holds in his heat but he's still out there rolling in the snow in subzero weather, happy as a lark, running to and fro with his bones and deer hides and marking his territory.
I think maybe southern flock owners are more likely to heat and insulate a coop when cold weather comes instead of letting their chickens grow accustomed to the cold.