Baking cornbread is the least demanding of all possible uses for a baking pan or skillet. The pan or skillet doesn't really need to retain heat. All it needs is a reasonably good non-stick surface. Cast iron's non-stick properties come from seasoning with grease, which is carbonized by baking. Carbon is indeed a good non-stick surface, but is very delicate. Soap ruins it, acidic foods ruin it, and too much heat ruins it too. The seasoned grease can also turn rancid after a few week's storage, and care must be taken to gently pre-heat the skillet until most of the rancid odor is gone.
Heat retention is the most desirable thing about iron pots and skillets. An aluminum, stainless, or composite skillet of equal mass retains heat just about as well as iron.
Having said that, I usually do use an iron skillet for my cornbread. It's a family tradition, and that's reason enough for me.
