"the DRM goes away in most cases." It seems to me tough that music is the exception to the rule. Computer games mostly have some form of copy protection. Most computer programs have copy protection, minimally with a serial number, many with activation schemes. One of the "features" of web applications is that it's practically impossible to pirate them. How can we know that ebooks will be any different?

With music and books, there is always the analog hole and then once one good copy is made, it can be duplicated forever. Also they are both naturally suited for self contained offline access which is less costly and cumbersome than requiring a network connection. So I think the parent poster is right and copy protection will not be successful in ebooks just as it was not with digital music files.