In my (UK) experience, public libraries charge for lending DVDs. But your main point is valid, I think: the cost-centric view only makes sense when there is a

In my (UK) experience, public libraries charge for lending DVDs. But your main point is valid, I think: the cost-centric view only makes sense when there is a free market, while in the market for a particular book, or even, in most cases, for a particular author, the publisher has a monopoly. So, if the people who buy ebooks are willing to pay more, that is what happens.