In France this effect is very visible as well. Many of my colleagues at the CEA (a very good research institute where many people from the French elite system work) had parents working in research as well, many of them at the same institutes, and I think if you'd look at the statistics in detail you'd probably see some strong bias for self selection within the system. That doesn't mean that the people in the system aren't very good (they usually are), just that it's very difficult for outsiders to get in. This in turn is probably due to the lack of knowledge about how the admission system works: While the centralized tests are of course fair in the sense that everyone gets the same questions, being well prepared for them takes years of preparation that already starts by selecting the right school for your children.

What makes me a bit sad here is that there is probably much more scientific talent out there that we're not tapping into by not providing good study conditions for everyone, and this is something that we must change.