I have no idea whether Europeans work harder than Americans, but I do want to say that you can't extrapolate the overall work ethic of America by looking at the SF tech world. It's a very, very small (and very privileged) microcosm of the country.
It's always a bit of a frustration running into constant comparisons, managers who want to emulate processes, and such when "Hey, you know what, we're not them... and we're doing well being ourselves." Not that you immediately dismiss new ideas because they seem to be from there, but don't just adopt them arbitrarily or operate like them too.
I have a sneaky suspicion that "most" of the American tech industry is NOT at all like SF / valley tech world.