Is that true? What happens when those 25% retire or can no longer work? Ahh: https://www.telegraph.co.uk/finance/personalfinance/pensions... - not too bad - the US got a C, UK got a C+.
Now back to the headline: $400 in available readies? You do have to start measuring somewhere when looking into poverty but it is harder than it seems on the face of it. Many people will drain their balance regardless to zero or below, (nearly) no matter how well off. I recall being a youngish lad with an income of £30 per hour - let's realistically say ~£50,000 per annum (gross, pre IR45). At that point in my life, I too would often qualify for "can't find £350" right now. My real point is that you have to be really careful how you measure this sort of thing, ie trying to quantify bits of people's lives with simple pithy statements.