Variable copyright is easier to enforce in selling printed books. International borders matter a lot less when selling a product that is downloaded than when selling one that is shipped or snail mailed. Right now Kindles only work in the US, but this will be interesting once Kindles and Sony Readers are downloading books wirelessly to many places in the world. If it's Amazon UK doing the selling, presumably UK copyright law will apply, and so on.
Life is about to get more interesting (or just plain complicated) for ebook sellers.
