I looked into this awhile back and the problem was that if you bought the US version and downloaded a book overseas on a cellular network there was a $2 surcharge for roaming fees. It just wasn't really worth it in my mind. Not sure if that is still applicable.

EDIT: Ok here are the new rules it seems http://www.amazon.com/gp/help/custom...T3Q#intservice Looks like it has changed so books are still regularly priced though other content is subject to a surcharge.