Agreed. 1000 songs is very different than 1000 books.
But consider it this way...the goal and benefit is similar: When you are choosing songs to listen to or books to read, you want a big selection. Many people want the big song library not to listen to them all, but to have broad choices. I think readers want the same thing. I'd love to have all of Gutenberg with me on a reader device someday. But I know I'm never going to read even a fraction of a percentage of them!