The "Read on Leanpub" view for readers who have purchased the book actually does this. The read online view for potential readers is one big scroll. (The reason for the difference is SEO and sales: we want the "for readers" view to be as nice as possible (i.e. page turn), but we want the experience for Google to see all the content as easily as possible, and we also want the "for readers" view to be nicer than the free one.)
To see the difference, contrast https://leanpub.com/markua/read (single page) with what it looks like if you buy it and click "Read on Leanpub".
This is the single page "Read Online" view, which is linked from the landing page:
By contrast, this is the "Read on Leanpub" view which is linked from the Library view of readers who buy the book: