I do agree from what I have seen Americans are harder working than European countries on average. However asian countires take the cake I think, Japanese, Chinese, and Indian people I think are definitely harder working. Its all to do with the cultures though, in Europe you have alot of socialist or at least very liberal countries and they subsidize laziness alot with large handouts to the unemployed, and labor laws that favor the workers. In The USA this is not so much the case, the minimum wage and welfare is really not enough to live any type of decent living on, so you are very motivated to work harder. However there is still some level of people feeding off the government and also societally laziness is seen as some type of "sickness" where its not really your fault that you are lazy, you are jsut born that way and its who you are. All the asian kids I've met would be more or less disowned by their parents if they didn't work hard whereas I see tons of American parents still paying for their 24 year old kids to go back to the sixth year of undergraduate education. Also I beleive asian governemnts operate on a similar principle and frown very bandly on those who are lazy, so there is a good amount of motivation to work.
Really I think all races are 95% exactly the same and ALMOST every difference between different races and countires is due to the culture and not the genetics of the race. Unfortunately some countries (like the USA and even worse Europe) are coasting on the achievements of their forefathers while others (like China and many East Asian countires) are actively bring themselves up form the third world. If this continues it is only a matter of time before they pass the Western world (although as counties advance they also tend to get more lazy, I ahve seen about obesity now being a huge problem in the Chinese upper class like it is in the USA now).