Earlier quoted context omitted.
US Federal Reserve studies indicate that the percentage of US households with no excess income after necessary expenses (as distinct from "ordinary expenses" as a term of art) is on the order of 10-15%. This definition roughly matches most people's intuition of what "living paycheck-to-paycheck" means. That isn't nothing but it implies 85-90% of Americans are not actually living paycheck-to-paycheck. There is another…
Are retirement savings considered ordinary expenses? If not, that could be a huge gap in this understanding.
I can't find precise data on retirement outflows and there are many possible ways to account for it (e.g. is Social Security contribution considered saving for retirement?) but what I can find seems to indicate that the majority of Americans do save for retirement, which would suggest it is an ordinary expense.
The only category of "non-ordinary" that I recall being surprising was eating out at restaurants. I should know better, almost no one ate out at restaurants when and where I grew up, but my perspective has clearly been skewed over time by my own lifestyle.