Users are not only giving to a charity and choosing the portion of the price they pay to a charity but they can also select from a list of charities to donate to. Thus giving some control to the consumer as to what kind of organizations they support.

The way Humble Bundle works is that it is donation based in that you can pay what you want for the bundle, with the minimum being a dollar. There are separate packages in each bundle that also ask for a minimum price, which depends on the "beat the average" price which is what on average has been donated so far..

Just as a user can choose how much to give to a charity out of the price given, they can also choose how much to give to the devs. So if one does not feel like supporting a charity for a certain bundle they can choose to give all of the funds to the developers.