What? Japan adopted representative democracy, human rights, capitalism, fractional reserve banking, the metric system, and even western attire. China is more authoritarian, but has made many of the same changes. Their economic prosperity is highly correlated with these changes.
And I'm flabbergasted that you think the USA doesn't prove his point. The original American culture was from the native Americans. Once it was replaced with British culture, the economy of north america flourished. In places where native culture was replaced with others (Spanish/native culture in Mexico, Portuguese/native culture in Brazil, etc), the people haven't had the same level of success. Similarly, Spain and Portugal haven't had the same prosperity as the UK. When it comes to per capita GDP, the effect of culture is vastly underestimated.
> [Citation needed] and so on, and so on...
He links to a citation in the sentence after your quote.[1] The paper is a study of the differences in cotton mill productivity in various countries. The author accounts for varying levels of technology, training, and other factors. He finds that the biggest factor affecting productivity is culture.
Honestly, I think you're reading this far too uncharitably. It's a blog post, not an academic paper. If the author took the time to address the objections in this thread, it would have been 10x as much work.
1. http://faculty.georgetown.edu/mh5/class/econ489/Clark-Why-Is...