He suggested the hypothesis that that's a reflection of the rise of the United States as a superpower over the last 200 years, and if anything were to impugn the United States' status as the market of refuge, those numbers would not be predictive of consistent long-run returns in the future.
That's a hard hypothesis to refute. Are there similar long-run numbers from all stable countries around the world, or is the US market unique in that aspect?