Books have been roughly the same for the last 200 years, since the printing press revolutionized how books were copied. Music, on the other hand, has changed maybe once a decade since audio equipment and the radio were invented and became widespread.
I think that people who read books, a small market to be sure, is made up mostly of people who go to a library to find out if they like something and, if the book is good enough, then go to Amazon or Borders or B&N and buy the book. I know that's what I do, and what a lot of other people do. Yeah yeah, anecdotal evidence, citation needed and all that, but I don't think the ebook reader is going to change the business any more than audio books did.