I suspect the reason is that in many countries, there is a greater focus on getting the fundamentals done with significant rigor. USA curriculums put more of an emphasis on breadth. I think they [the Russians] are right. For STEM-focused students, there should be no short-cuts when it comes to mathematics curriculum.
Good read.
I searched for "Russian mathematician's experiences coming to the United States and the culture shock with respect to education" ;)
Also, if you look around and individuals who are staffing the top hierarchies of business/market institutions, what kind of credentials are most commonly seen there?
On top of that, in even intellectual subcultures, what stripes of intellect tend to be most respected in US culture?
I think there's a number of ways (some subtle, some less so) in which American society messages people about the status of STEM and in particular about the M, which is almost always about its auxiliary value for something else and rarely respected in its own right.
I think it's plausible there are a number of features of a communist culture that might shift some of those incentives, especially when combined with a generally more intellectual culture.
(Also, this shouldn't need to be said, but this is not an argument about the general superiority of communist society. I suspect that more pragmatic societies do better than more ideologically organized societies.)