This research is fundamentally flawed. Somehow Chris thought that all .com domain belong to U.S companies, which is very very not true. The result is a lot of other country's traffic are credited to U.S.
Just an example, Baidu.com, the search engine that has more market share in China then Google, is a top 10 worldwide traffic website. But it's counted as a U.S company in Chris's graph.
Of cause, this may or may not change the conclusion. But this research has some fundamental flaws on collecting data which make the result useless.