another point is that in the US the notion of "Hacking" is still seen as negative or criminal.
Something else is that in that age group in the US people are about to graduate or graduating so if they are really good at math/science/engineering they have already either been picked up my companies or in the process of getting hired. Why does this matter? Becuase if you are going to or are working for a company im pretty sure they dont want you to participate in any event about hacking.
I think the phrase "hacking contest" was how the author of the article chose to describe it. The TopCoder competition page doesn't mention the word at all: http://www.topcoder.com/tc ; probably exactly for the reason you describe.
Something else is that in that age group in the US people are about to graduate or graduating so if they are really good at math/science/engineering they have already either been picked up my companies or in the process of getting hired. Why does this matter? Becuase if you are going to or are working for a company im pretty sure they dont want you to participate in any event about hacking.