My read on this is that the genetic component is much more significant in the US than in other places... because the US is significantly more economically stratified, nepotistic, and has a broken education system where rich idiots can get all the education they want, and skate by, but you basically have to be a diligent and lucky genius to escape poverty and the shit-tier education it has bestowed you with.
Thanks for the study. I will review in more detail. I don't agree with your conclusion here. Greater association between success and IQ, as we see in the U.S., would imply a higher degree of meritocracy. That is, more intelligent people are better able to break through class barriers due to their performance. This study implies that Europe is more hierarchically stratified, and that one's abilities are not enough to make any difference in success. To be honest, I wouldn't be surprised if this were the case.