Once you have a significant online readership, then you might successfully argue that you have a captive audience for any books you author. But your captive audience probably needs to be at least 50,000 visitors per month, if not double that, to merit the interest of a commercial publisher. And by that point, you may be far more interested in self-publishing! Book Proposals in the Digital Age
Booking produces relationships. Booking is a process that connects readers, authors, characters, ideas, and stories into complex webs. There will be a million ways to weave these relationships — including the ancient path of a linear story that runs interrupted on deadtree paper. But that is but one way to weave the web. There are other bookings that favor the reader’s powers, and yet others that leverage sharing, and yet more relationships that take years to complete. We have not yet begun exploring the possible ways to book. The Technium: Post-Artifact Booking
The ideas are there; the talent is there; the readers are there. But when the three come together, inevitably someone else can figure out a way to use the technology for a different end. The better and more experimental it is, the more likely this is true.

Why we’ll never have innovative e-books - CNN.com

Technology is there to drive incredible advancements in eBooks beyond just reading them on a Kindle. Why hasn’t it moved forward? Wired thinks it’s because the technology keeps getting applied to other areas. Maybe, but sooner or later the tools will get easy enough for everyone to use - like happened with blogging - and the floodgates will break.