The difference between 78 (US) and 80 (many countries of western Europe) isn't large enough to be a big deal, considering it's below 50 in most of Africa, below 60 in most of the developing world, only 65 in Russia, lower than 78 in much of eastern Europe, and 78 in Britain.
Infant mortality, homicides, and drug deaths in our inner-city ghettos likely bring the averages down a couple of years. Since most Americans don't live in the ghetto, I really doubt there's a difference between an average middle-class American and an average middle-class western European. Ours could even be higher.
Hope this helps.