Looking at Energy Use in US Residential Buildings

I think you're underestimating how much house construction has changed in just the last decade or two. Most detached houses are still stick framed, but the similarities end about there. Modern sheaving has integrated waterproofing membranes, air and water sealing tapes and fluids are applied to to all envelope intrusions, advancing framing is becoming common with 2x6 studs 24" on center to allow for more insulation, HRV/ERV integration into the HVAC system, continuous exterior insulation and blower door tests are required by code in most jurisdictions, I-joists and LVLs dramatically reducing the amount of solid wood and steel required to hold up a house, and the list goes on. The exteriors often look much the same for neighborhood character and consumer preference reasons, but the finished product performs dramatically better on energy consumption. That isn't to say there are not still some houses built with truly awful quality, but modern building codes are driving significantly better energy consumption. We then give back all those gains by building 4500 sq ft mcmansions to house a family of 3.