I agree, if by "eBook" we mean only the specific formats (ePub, PDF, mobi). But I'd argue that you can have all if you make a website instead, and read it on a browser. You can then have multiple tabs, bookmarks, large pages with fast scrolling, etc.

And an epub is just a collection of HTML files anyway, so it shouldn't be difficult to make a website instead. I think what's missing is a "website archive format" supported by all major browsers, so the user can have an offline copy of the "book".