Actually that is exactly the idea behind HTML (web pages) and ebooks. HTML was designed to display text in a scrollable manner wherein the user could adjust the text size and font family. Ditto (almost) on ebooks. We might not always have font family control, though we should, but ebooks are basicaly HTML that is formatted for reader software (a specialized browser purposed especially for viewing ebooks) and should reflow as the text size and/or font family is changed by the user. Your analogy of ebooks as scrolls (but with added hyperlinks) is right on. Ebooks are in fact modern, hypertext versions of scrolls.

PDFs don't fit this analogy, but then PDFs were never intended for viewing in the same manner as hypertext (HTML) and thus they do not lend themselves well to readers designed to display hypertext.