I don’t think this is a case of “have to”, I think it’s a case of “want to” and recognition of those people who make your site what it is. Let’s face it, all the content on a typical Q&A site is created by the users. Why shouldn’t they share in the profits?
It’s not an easy thing to set up and make work. You have to have a good infrastructure and watch out for the inevitable gaming. But kudos to Calacanis and Mahalo for making it happen and I hope it works out well for everybody.