I've bought a few e-books which are copies of pbook I already own, but in most cases it was because it was a favourite and my copy was a few thousand miles away
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In any case I've probably bought paper copies if I hadn't.
I've thought about replacing some of my collection with e-books, but have been stymied by two facts. Price and availability.
I've normally bought books (Paperback or hardback) when I could get them on sale or discounted. I can't justify paying full price for a version which is more limited and can't be resold or lent out.
Also a large number of book where I might be willing to pay the price are not available for purchase. So that removes the option of doing so.