Earlier quoted context omitted.
While it is true, they have minimum pricing, if you want the items without compensating the publisher for them, you CAN stiff them. For instance, you can change the sliders so 100% of your money goes to charity, and then you didn't pay them for the books at all. Sure, not what you want, but worth noting. Particularly useful if you want something on offer, but don't like the company selling them and don't want to supp…
This model blows my mind - I just cannot quite work it out. Have the companies involved - O'Reilly and Humble Bundle Inc - just decided that they're OK with potentially making nothing at all from this, so long as lots of money goes to charity? I mean, it's wonderfully altruistic, and I suppose it could be a lot more complicated than I'm giving credit for (does the goodwill gained by them outweigh the financial hit?)…
15% of whatever money you pay doesn't go to a charity, it goes to them. This is not explicitly stated. See here: https://en.wikipedia.org/wiki/Humble_Bundle (search for 15%)