We also have to take into account that we (at least "I") selected breeds that are heat hardy (except my marans), not cold hardy. It was supposed to get down to 29 last night, but this morning it was still in the 30s. Whew. I had to put tarps and sheets over my open coop, and they all seemed okay today.
I was on a thread yesterday started by another Floridian asking about trying to keep their chickens warm, and a lot of times people are making an apples to oranges comparrison when the give advice. A bird in Alaska is a bird in Alaska, where it is never very warm, and a bird in Florida is a bird in Florida, where they aren't used to the cold. Ever. And yes, the humidity makes a differnce. Even my brother will comment on it when he visits for the holidays - from MINNESOTA!
All I'm saying is to be careful and take into account your own, unique situation. I just read a thread by a guy in Tennessee that lost a few birds last night due to an open coop and ususually cold weather.