To add on to what Manish said, it's important to us that the core docs remain free and accessible, which is one of the reasons why it was great to work with NoStarch; they're super happy to keep the book 100% open source. Win-win.
In addition, the plan is to donate the proceeds to OpenHatch.
The No Starch shopping cart is having issues for me. I'll come back later in the day and try again. I got to "Review your order", then "You have no items in your shopping cart."