Here's why I find this potentially exciting. Right now a publisher takes a risk in publishing a book. They have to guess how many copies they should print. Print too many, and the books take up space in a warehouse; don't print enough, and bookstores run out, and (potentially) sales are lost if the reader can't get the book when they want it. Having the book available for sale online via POD means the customer can always get the book but there are not unsold copies lying around. This could mean publishers would be more willing to risk publishing books by new and unknown authors.
Of course, the downside is, it pushes more sales to online, which publishers don't like because they don't want Amazon to control even more of the market. This may considerably slow down the adoption of POD for big publishers. Publishers could always sell direct, of course, but they don't have much of a built-in online customer base compared to Amazon.
Barnes & Noble has their own POD online service for self-publishing called Nook Press Print. I wonder if this could push Barnes & Noble to either create a publisher version or add more Espresso Book Machines to their brick & mortar stores? Or both?
We live in interesting times.