What was happening was that a bunch of authors were gaming the system by turning out really short shovel-books, and depending on the fact that people weren't giving up on the books until after they had gone through the 10% minimum read to get a payout. (i.e. you publish a 50-page piece of junk, it only wastes like two minutes to go through five pages.)
Price-per-page is a lot more fair for everybody. If you, author, can't hold your reader's attention to read more of your longer book, write better books.
Given how the total payout remains the same, it's hard to argue that the new method is a worse way of splitting up the pool.