Nick Carr explains how ebooks can be revised after publication:
One of the things that happens when books and other writings start to be distributed digitally through web-connected devices like the Kindle is that their text becomes provisional. Automatic updates can be sent through the network to edit the words stored in your machine - similar to the way that, say, software on your PC can be updated automatically today.
My last book, whose first print run was bollixed by HarperCollins, would have been salvageable. Stephanie at UrbZen gets paranoid about retroactive censorship.