There are good and bad ways to present text in books and this is not some subtle improvement, this is noticeable. Typesetting books is seriously hard and there are tons of pitfalls, even if all you need are paragraphs and chapter headings. To make this short, here are all things books can do and the web cannot (yet or in most browsers) do: Complete control over the font. A lot of microtypography. Complete control over justification. Easily creating and maintaining a rhythm.
I'm sure there are a lot more. (Those points are also the reason why typography in ebooks still sucks for the most part, some of that is caused by the ineptness of those who create those books.)
Anyone who has ever had the book of someone with no design background in their hands will be able to testify that there is a huge difference between books done by a professional typesetter and an amateur (if that amateur isn't self-taught and doesn't otherwise care about design).