Why do Americans make more money in software?
* Pure inertia from the early cowboy days of Silicon Valley, which gave us great universities and lots of private investment capital looking for returns. (Contrast with academic grants.)
* A more straight-forward focus on technology-for-moneys-sake (really anything-for-moneys-sake) and marketing
* The U.S. development culture, to Dijkstra's eternal chagrin, is much more "Worse Is Better" so we tend to ship early, often and win the market, even though our stuff kind of sucks.