According to yesterday's article in the NYT, this trend of the US's not keeping up with this group of 14 wealthy countries was absent in 1950 and only really started picking up steam after 1980. Since the US population was already significantly more heterogenous in 1950, why didn't that heterogeneity show through in the life-expectancy data for 1950?
The difference in heterogeneity between the US and the other countries has probably increased from 1950 to today. But I also suspect that some of this difference in life-expectancy between the US and the 14 others is that it might be easier to implement preventive health care measures that reach the whole population in societies that have more comprehensive health care insurance by default.
It would be really interesting to see data comparing the healthiest people in the US and other similarly developed countries.