It seems to me that it is essential to have the entrepreneur's DNA in a population in order to grow an entrepreneurial environment, and therefore a successful startup ecosystem.
The right parameters should be driven by the need to own its own business, to start something of personal value, to build something of personal pride, to seek independence, to pursue achievement (monetary or otherwise) . All on a voluntary basis, and not necessarily out of desperation.
The chart shows that many smaller countries such as Norway or Australia have populations driven by entrepreneurship. However the argument that Americans are more driven by entrepreneurship than the Europeans or the Asians is wrong, when you look at the % of the population of the country as a whole.
The only reason it seems that the U.S. drives more global entrepreneurial success stories is because it has a large domestic market, that gives immediate and substantial traction to startups, and two, the readily available pool of angel and venture capital, not present in other countries.
If we were to regroup all the European countries, the data would be very different but their markets are still fairly fragmented (language and culture), which proves the Eurozone still has a long way to go to become a single large market for startups.
Brazil and China, the two next largest market blocks, are fast rising but still too far for probably another generation or two. This is mostly due to availability of risk capital and sophisticated entrepreneurial talent.