Fridges did become energy hogs in the 1970s and 1980s, the defrost cycle being one of the bigger consumers. Customer satisfaction was considered much more important than energy conservation, so overkill was common.
One relatively simple thing you can do with older fridges to reduce the energy consumed by defrosting is to connect the defrost timer to the compressor instead of the line. Then, instead of defrosting, say, once every 24 hours of real time, it'll defrost once per 24 hours of compressor run time, saving a whole lot of energy in winter, spring and fall, in the summer in moderate climates, and in air-conditioned houses.
Switching from fiberglass batt insulation to injection-molded polyurethane foam cut heat gain by about half. That mostly occurred in the 1990s.
There's still a lot of energy savings possible, but most appliances are marketed based on first cost, not energy savings. The SunFrost people provide the counter-example, using perhaps 1/10 as much energy as conventional fridges.
Sun Frost energy efficient refrigerators
