Heating isn't a major concern. Many houses have electric heat because it just isn't worth the cost to put in something more efficient.
But air conditioning is needed a large part of the year. And in the summer it gets quite hot, so electric bills can be very expensive. So in any newer construction, there is a lot of effort to make things energy-efficient. Houses have double-pane windows, radiant barriers, thick insulation, and leak tests to make sure that hot/humid air from outside cannot make its way in.
There are certainly older buildings that aren't very energy-efficient, but around here I don't see that as being because of air conditioning.
Step 1: It is too hot/cold here
Step 2: Lets put in heating/AC
Step 3: Damn, the electric costs are getting too high. Lets put in insulation and double-pane windows (well, actually three-pane is standard here in Sweden) to keep down the costs.
The further you live to extreme heat or cold the faster a society progress down the ladder. Which is also a reason the death rates during winter is a lot higher (per capita) in central Europe than it is in northern Europe - people in the northern parts have long since been forced to learn to build better houses whereas people in mild climates can afford to fail as it isn't that many days a year that it is a problem.
Have any part of Texas considered central cooling? It should be even more effective than having units in every house as long as it isn't too damp and the water needs to be removed as well. But perhaps that kind of solution would be too socialistic for you :P
EDIT: Seems like this is true for all european countries
I find that hard to believe. Where I live the local muni delegates to a state wide "uniform dwelling building code" I googled it for laughs and the minimum ceiling insulation as of the '09 revision was R-49 which is about 14 inches of fiberglass.
My concrete block basement walls met code 50 years ago at about R-2 insulation value, as of '09 the mandatory minimum for new basement walls is R-15, OK then..
The biggest problem I see with post-AC era houses like mine is very poor cross ventilation. I must run the AC when its 60 degrees outside because the windows are not oriented for cross ventilation so I will roast alive at 85 degrees indoors when its 60 outside without AC.
I do agree that having the house designed for good airflow in the first place would be ideal.
Condensation is the real killer if you live in a humid climate. It damages the walls, causes mold, and can even mess with the electrical system.
Older houses (in my area, that's early 1900s, laugh away you European readers) were built with huge beams of old-growth timber by careful craftsmen (sometimes in the Craftsman style, sometimes colonial or victorian). Houses this old typically had antique plumbing and electrical service, which needed (or now really need) upgrades, and they also will likely need window and/or siding replacement. During these repairs and remodels, smart homeowners and contractors also upgrade the energy efficiency, and there's a very strong skeleton on which to do so.
Shortly after WWII, there was a lumber shortage. You can drive around and identify the neighborhoods which were constructed in the late 40s and early 50s because the eaves only project a few inches out from the walls. These were built as fast and cheaply as possible. But for a while, energy - especially for heat - was cheap, so they kept building them.
Since then, energy has become variously more and less expensive, and manufacturing/construction techniques have produced cycles of lower quality cookie-cutter cost-optimized goods and higher-quality standardized, well engineered construction. We're riding high on an efficiency swing right now, to the point of absurdities like homes so well air-sealed between Tyvek, caulk, and air-tight electrical fixtures that you're required to install an air vent to the outdoors in the furnace room to prevent negative pressure problems.
My house has a large, paper-thin southern wall and during the summer it gets so hot that it radiates heat into the house at night. So I have to air-condition my bedroom at night. And the windows are stupidly designed, so when the wind blows in the winter I can feel it enter the room - and again I must use electricity to keep the room warm.
Thankfully, "green" building methods are starting to change this wasteful attitude.