So your not really supporting the charity if you do it?
The original challenge rules were for you to donate to charity or take up the challenge, which had a caveat of you donating money in the name of the people who accepted your challenge. The idea was to simply pay, or promote awareness as well as potentially create more funds for the charity.
Since than the rules have been altered to fit numerous charities, some rules state a given amount you must donate and half of that amount if you partake in the challenge. These rules were still effective, in the sense that even if you only donate half buy accepting the challenge you make up for it by bringing more participants into the game that can than also promote awareness as well as donate to the charity.
Of course as everything does, it has been bastardized to just simply be a game that has no ties to donating money or have people who think that by participating in the challenge the are performing a public service by creating "awareness" but never letting their wallets support the cause.
I have no idea which version of the challenge they are abiding by. But I have to think they donate their fair share to charity regardless.