In an ideal world, people without a lot of discretionary income are given the electronic edition (which costs [nearly] nothing to distribute) for free. They act like the breezes that loft the dandelion seeds — they go around, telling people about the book and its merits. In this regard, they’re better than random breezes, for they undertake a directed distribution of the book, seeking to bring it to the attention of people who are likely to have a positive response to it.
Once the book lands in the hands of someone who does have discretionary income, that person is given a multitude of opportunities to engage in a commercial transaction with the writer and her publisher. These range from buying the book (which has many positive externalities, such as improving the book’s sales record and hence increasing the writer’s next advance and other stores’ orders of her books) to buying limited editions, memorabilia, tickets to a lecture or reading, etc.