I'm not sure how different this is from the existing situation - where if a hardback version of a book contains errors, they get fixed in the paperback, or errors get fixed (sometimes) in a subsequent reprint? In other words, you only get the fixed version if you buy the book again. Of course with ebooks things could - and should - be better, but this strikes me as more of a missed opportunity to take a step forward rather than an actual step backwards.