When you talk about "the Chinese" you're talking about somewhere between 3-4x the population of the US. Now, the US has the advantage that historically, smart people from all over the world (including China) have emigrated to there. The Chinese also have the disadvantage that a lot of intellectuals were murdered there during the "Great Leap Forward". Even so, their culture presently values education and engineering, so I'd argue that the difference is merely now there's sufficient penetration of Internet technologies for more Chinese to enter the competitions in the first place.

Maybe more and more people are getting access to computers and to decent learning material and universities?

But websites in China really suck,where are these contest winners?

They now have English keyboards.