Which part of 20th century was the same for Europe except work ethics? America did not had two world wars on its soil, that alone will make majority of that century different.
That is account of worked hours, not that everything except worked hours was same on 20th century - which is what I found suspicious.
I agree that Americans on average spend more time in work.
More conrroversially, I also think that the notion of work ethics should count in also what you do at work and crunch stories about people sleeping under table should not count as better work ethics. E.g. more hours less effectively is not better work ethics. (That is not to imply American companies are less effective per hour, I don't think that is the case.)
It says Americans work 25% more. This is usually the conclusion of this kind of thing.