Your point about science is roughly correct but cannot be taken too far. A country's average will indirectly influence the R&D activities of the top group as we

Your point about science is roughly correct but cannot be taken too far. A country's average will indirectly influence the R&D activities of the top group as well. Democratic support, educational funding, social perception all influence science career to an extent. For example, it is so much easier to rest on your laurel when everyone around you does much worse. And when the average performance of a group is raised even moderately, the number of people who passes a certain threshold increase substantially (assuming a distribution not too far from Gaussian). Also, there needs to be a critical mass of good researchers to create a rich ecosystem that in turn produces significant technology. The US lead in R&D is partially caused by its large number of active researchers and the collective amount of funding these scientists receive compared to other countries.