Not to drag Apple into this, but
I remember when Steve Jobs introduced the 2nd AppleTV, which only streams content. He said basically that his customers want to own* their music, but want to just rent their video content-hence the two models (buying iTunes music, streaming iTunes video). Based on how Apple is treating iBooks, I think they (and many readers here) put books in the "own" not "rent/stream" category, which is why the Netflix analogy doesn't seem to work here. (I understand the analogy, I just think how the content is used is more an issue than you think-even Pandora is probably used as a radio replacement rather than a CD collection replacement)
*yes, it's a license, not owning blah blah blah