Thus would per capita GDPs match, I'd expect twice as many poor...

No, because then the level of poverty would have been different, see. ;) That's the problem with that kind of measurement.

and that's not considering differences of measurement and unaccounted-for factors (like stuff the French poor get for free but the US poor have to pay for, say, healthcare).

Right. Which is why I before use HDI is variable, because it does take those factors into account. And United States are in place 8 and France in Place 16.

Both high enough to be practically the same in a global perspective. Which is my point. Poverty isn't caused by having a choice in pension schemes, or having private pensions. No matter of wriggling and juggling with facts is going to change that.