Originally Posted by daffy4u
It's been ruled in court that a "permanent license to use" is a sale, regardless of what the seller calls it. The seller can't demand that there's no resale rights, or that the purchaser cannot allow others to view the content.
This relates to two cases: one where someone was reselling boxed software on eBay, and the company wanted to claim copyright infringement (how, I'm not sure; it was the original box & CDs being sold); the ruling from that drew from an older case involving movies that had been sold with the criteria that they couldn't be resold or watched, and other movies that had been sold as cellulose scrap and the producers were outraged to discover that some of them were being resold as movies, not as plastic.
The rulings hinged on the concept of permanence: if there was a schedule or expectation of returning the content, it was licensed; if the purchaser was not expected to return it, it was a sale.
(Since digital content is rather ridiculous to "return," I think it's likely they'd assume time-limited DRM as the "return" policy--hence DRM'd library books are licensed, not sold/given away.)
Since Amazon makes no claim that the books must be returned, or deleted, after any particular time, nor in a given set of circumstances, they're sold, not licensed. Amazon is lying to its customers in the hopes that none of them will have big enough lawyers to challenge that.