"GitHub must be allowed to use the code commercially without restriction, regardless of the license choosen."

I'm not too crazy about this. Contests can be good and bad at the same time. "Here guys, solve this very hard problem for us for free and we'll take it off your hands and we'll completely ignore your licensing wishes and use it without any restrictions whatsoever."

I envision a lot of "Well if you don't want to participate, DON'T!", but the point of the matter is, I see GitHub as taking advantage of a warm and supportive open-source community. The license of the submitted code should apply to everyone, including GitHub!