While that's partly true (modulo certain exceptions such as the cost of living varying quite a bit from place to place), the comment you were replying to was making a point about the cost of college. Which has grown so much faster than general inflation that it's in its very own category.
I guess I don't see how we can meaningfully measure cost of living without taking into account cost of education.
If a salary these days only puts the kids through high school, then the standard of living that salary buys has fallen drastically in practice.
My BS comp sci degree was a waste of time, to be real. Fairly certain my first job out of college would have been appropriate for myself as a high school senior. One of my parents and two of my grandparents were programmers without needing anything more than a high school diploma. Despite the push for trades, I couldn't even get an interview without a degree even despite my experience. Add in the increase in the cost of living, stagnant wages, plus inflation and it doesn't make a pretty picture.