While one can mock the US for their sporting achievement dip, it is relevant to note that a large percentage of the North American athletes such as the Jamaicans, use the US universities and coaching infrastructure. The universities are welcoming to foreign athletes, just as they are to foreign students. Many innovations come from the US too -- e.g., the speedo swimsuits which were designed with NASA assistance, the ethical use of which is a separate story. The games are heavily funded -- and telecasts and times therefore manipulated

-- by NBC, an American company. Most of the big sponsors - vital for many top class athletes - are US companies.
The Chinese surge, while clearly impressive, is representative of gaming the system perfectly and building a large enough pool of talent with all the support, world class infrastructure, expert coaching etc. and starting from a very young age. The Chinese have proven that anything can be achieved with will and extreme hard work. The US edge
can be has been blunted through such large-scale dedicated effort, and the US has no such 'Marshall Plan' for sporting domination through regimentation, and never will. So it is not surprising at all.