I don't believe the goal at this point is to be the Netflix equivalent of books. This is an incentive to get people to sign up for Amazon Prime which should translate into sales across the other realms (purchasing, videos etc..). If you look at one book a month that's about $6.50 per month which might still be making Amazon a profit depending on their margins, especially if they purchase other products as a result. This is a stepping stone and a feature of Amazon Prime only - it's not for people that read 10 books a month nor is it to replace their book library.