The clincher may have been the fact that rather than receiving an advance, it was me paying iUniverse the initial fee to publish the book. Seeing who writes that first check is as good a way as any to distinguish self-publishing from traditional publishing. It is simply a matter of limited resources. My publicist has been working away trying to get some reviews and reports that she is getting some good responses, so I remain optimistic. Not having to deal with returns is a big win for iUniverse.
Someone wishing to purchase the book can certainly walk into any bookstore and order a copy.
But that implies that they found out about the book some other way. Ingram offers a program called Ingram Express that effectively has it sell your books on consignment. Ingram warehouses them and reorders as needed, but can return them to the author at any time, which means that Ingram allows booksellers to return the books to Ingram. But both are only available to those who still own the rights to their books. The reality is a bit different.