The result? Publishers churn inventory faster than ever, continuously produce "new" editions of successful titles in order to re-start the three-year depreciation clock, and give the average new release a 6- to 8-week shelf life. This means there is an enormous amount of waste in the system, and this waste has to be paid for somehow, and by someone.
By the way, when Barnes & Nobles or Borders "returns" a paperback book, they don't actually return it for resale or recycling. They just tear off the cover and send the cover to the publisher, and chuck the rest of the book in the local landfill. Ironic, innit?