"Amazon has managed to dominate the e-book market by offering its Kindle e-book readers at a very low cost"
That is true if you look only at readers. The Kindle ap is free for the iPad and iPhone (and I assume Android devices), so most people buying the e-books never buy a reader.
It does not take a genius to see that the launch of the new Smartphone by Amazon is a move intended to both directly and indirectly boost the sales that it makes at its online stores. All those sensors and cameras are not just to make the customers feel better but to let Amazon know exactly what to suggest to them; targeted marketing at its best. If you intend to use the Smartphone specifically for shopping at Amazon then run and buy this one but if you actually need it for other internet based services then I doubt you will love (or even like) this phone.
Targeted marketing is not just about identifying the audience or prospective customers who are most likely to be interested in and to buy your products. A bigger component, following the identification of this audience, involves researching into them in order to understand their specific needs and interests so as to serve those better. In the world of modern internet marketing and based solely on these two scores, there is no Smartphone in the market today that can rival or even come close to what the Amazon Smartphone promises to offer.