Page numbers aren't the only method of marking off measurable sections of text. They just make the most sense when you're dealing with physical materials that are laid out in page form. When books were nothing but rolls of parchment tied up with ribbon, page numbers were not the method used to refer to passages of text. Therefore, when page numbers are meaningless (as with etext versions), when it becomes bothersome enough to folks, a standard method of referring to position in text will be agreeed upon, and it may or may not be page numbers, but stating uncatagorically that it *will* be page numbers is just silly. Sure, page numbers are what folks are most familiar with now, but I doubt the middle ages (before printing presses existed) the monks who copied texts used such concepts. So, something will grow out of the need for marking places, but I'm not convinced it will be page numbers. (bookmarks aren't just used for keeping your place in a physical book anymore) There's nothing keeping the publisher from inserting bookmarks in their digital copies, then folks can just refer to bookmark 8, or bookmark 27 when discussing material, thereby removing the need for page numbers, since bookmarks can occur anywhere the publisher wants them. Of course, you'd need to distinguish between publisher bookmarks, and customer ones, but that's rather trivial.