Earlier quoted context omitted.
The article also doesn't mention an obvious bias, that is, if a startup starts in Europe, there are a lot of incentives for that startup to move to the U.S. early in its life cycle. In that scenario, the startups who become successful (and who originated elsewhere) all get counted as U.S. successes. This would vastly undercount both the total number of startups elsewhere as well as the number of successful startups.
This is entirely correct and I know several founders who did so, but thats not really the point I am trying to make (which admittedly I didn't make well) The question that still stands is why they are moving the the US.
Investors are looking to fund companies with global reach that will break down communication barriers, render national boundaries meaningless and bring us all close together. . . as long as they are located in California.