Jordan Weissmann lays it out clearly:
Still, reading a book digitally and reading it on paper remain almost identical experiences. Digital books aren't much more visual, they don't tend to have more movies or interactive features, they don't typically connect you to the community of others reading the book. It's just a book, on a screen.
Partly, that's because books are currently written for both pages and digital editions, and neither authors nor publishers want to put huge effort into features that can only exist on the digital platform. But it can't be long till that changes.
GoodReads might be a start toward at least changing the social experience of reading. It's easy to imagine a Kindle program that lets you toggle into the forum for your book, or even your chapter, at any time while you're reading. Adding that social aspect could, for people who wanted it, make reading Kindle editions a dramatically different, more communal experience than reading print editions. And it wouldn't require any changes to the print edition at all.