I'm guessing it's a ton of heating because houses are very badly insulated, both for historical reasons and because otherwise everything rots in hot and humid summers (and nothing ever dries completely).
Japan has the same issue (insulation is quite terrible throughout, central heating is also rare), I'm guessing Houston is even worse because people keep to western habits (light-ish indoor garments and heating the whole house).
IMO, we need to start designing the equivalent of energy star ratings for new construction as there is a lot of low hanging fruit out there.
To me, minimizing temperature variance is a much more useful goal than say "hey solar!"
People care about $ so they care about energy costs. If you just show them people will make informed decisions where now it's all up in the air.
EX: Heating and cooling costs for the average 3 bedroom hose in this area is X to Y$ per year, this house is estimated at: z$.
Another advantage of this approach is most savings shows up at the low end of the scale. Where LEED and other green certifications focuses on the high end of the scale which has diminishing returns. EX: Over 100,000 miles 10 vs. 11MPG saves 909 gallons, where 40 vs. 60 MPG only saves 833 gallons.
We did have a neighbor who contracted with a propane company to fill a residential tank, which was used for heat and cooking. But that wasn't common in the neighborhood.
In Tallahassee, the places I rented didn't have gas, only electricity. Eg, pulling up rental housing in Tallahassee, https://www.rentrange.com/tallahassee-fl/o-3316-calumet-nice... says it has "Electric heating". Searching for Atlanta, I found http://www.cbs46.com/story/21444870/atlanta-fallen-tree-leav... which says "'Fallen tree leaves Atlanta residents without lights and heat' ... "My house used electric heat so it's cold".
Rather than be anecdotal about it, I found "Space Heating in U.S. Homes, by Climate Region, 2009" from http://www.eia.gov/consumption/residential/data/2009/#sh . Of the 19.1 million homes in the "Hot-Humid climate region", 12.4M use electricity, 4.6M use natural gas, 1.4M have no heat, 0.5M use propane, and the others (fuel oil, wood, etc.) are too small to be meaningfully reported.
There is an apparent conflict between your observations and this survey (and with my own observations from living in Florida).
GA has 1.7M homes heated with gas, and 1.7M heated with electricity, out of 3.5M. That has the highest percent of homes heated by gas.
In FL, and in line with my observations, has only 0.4M heated with gas, and a whopping 5.7M out of 7M heated with electricity. That's the lowest percentage, which is reasonable for a place with little need for winter heating.
Overall in the South, some 13.3M homes are heated with gas, 24.2M with electricity, 0.6M with fuel oil, 1.9M with propane, 0.8M with wood, 0.2M with kerosene, and 1.0M have no heat.
> Everywhere but Northeast, fewer homes choose natural gas as heating fuel
> EIA data show that homes built since 1970 use electricity and natural gas as their main heating fuel in roughly equal proportions.
> The South is the only Census region where electricity is the main space heating fuel in the majority of homes.
The survey data is at http://www.eia.gov/consumption/residential/data/2009/ .