I can see the advantage for people who like to take plenty of reading matter on holiday but don't want to pay excess baggage charges for the privilege!
Like you, I'm a bit surprised that the e-books aren't cheaper, after all, there will always be a demand for the real thing because there's something special about the feel and smell of a book (unlike a CD), but I imagine like everything else, prices will drop, especailly when they start circulating on p2p file sharing sites, which is surely inevitable?
Of course, you can download e-books to read on your PC, laptop, netbook, iPad etc., the only difference I can see (apart from compactness of course) is the e-book reader uses "electronic ink" to avoid eye strain and glare - but my monitor has a setting for reading, which I presume does a similar thing.