That S&P 500 companies' international sales barely trail domestic sales is one of the more amazing stats I've seen in a while. The first thought that came to mind was iPhone sales in China. And while China's growing consumption has likely been a very large contributor, the pie chart above doesn't signal that international trade is too China-heavy.
It can't be a coincidence that the percentages above are strikingly similar to the breakdown of the world's market cap (i.e. the percentage of publicly-traded shares by companies' domicile). The world is truly a global marketplace.