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Amazon: Older Kindles can no longer download e-books
(www.heise.de)
This is a most excellent place for technology news and articles.
It's true that normal books do experience wear and tear, but looking at what my local library has I'd say that many or most can still least many years before needing to be retired or replaced.
As we're seeing with Amazon, with ebooks it's really the readers that expire over time