That's a little silly! Not required for Amazon or Lulu...
Also EPUB is very limiting. They tried so hard to make it like real books, that they forgot that it's a standard for computers. Sound, interactivity, scripting, SVG, all the fun things got left behind!
ePub is the best standard we have for ebooks at the moment and it's rapidly becoming the industry standard with Amazon the only last major book store without support for it.
Sound, scripting, interactivity can all go into an application instead. Not everybody want those "fun things". Ebooks should stay to the art form of the books reading, just textual based with images, nothing else.