What I'm struggling with is the idea which seems to be being expressed that, having paid for a book in one format once, you're entitled to free copies, for life, in any other format that you wish
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All my very favourite books - the ones I read and re-read - I've probably bought multiple times; sometimes because I've initially bought a paperback and wanted a nice hardback, sometimes because I've simply worn out the original. I don't consider that buying a book in one format gives me some "God-given right" to "eternal use" of that book in all conceivable formats. If I buy a hardback and want a paperback, I have to buy a paperback (or vice versa). I honestly don't see that an eBook is any different.
Perhaps it is just a cultural difference. For all I know, people in the US routinely photocopy their paper books and read the photocopies, because their "fair use" law says they can. Here, we just accept that books wear and, and go and buy a new one if we want an additional copy, or we want the book in a different format.