Reversion to the Mean. Doesn't look like anytime soon frankly- I would estimate Chinese GDP will exceed that of the USA by 35%+ before that becomes a factor. But growth rates will most definitely slow over time.
Looking at the graph, notice how the rate of GDP growth accelerated around 1992- that's the year I moved to HK! But na- it was the Deng factor. A man small in stature, but possibly the most significant person of the 20th century. Long March survivor too.