It's just that some countries started out with a better standard of living than others.

Increasingly it looks to me that the capitalism then is more different from the capitalism now than from socialisms then. If economic deterioration for the masses will continue everywhere, the 1970s will look like a golden age for any country. That does not necessarily mean that socialisms were keeping up with improvement of living standards by themselves, as Western technologies "found" various discount ways to the socialist block. But living standards were indeed improving basically everywhere (except perhaps South America), dynamically or "slugishly", sustainably or not.