The many comments I have seen ask why not buy the audiobook instead of using the Kindle "robotic" text reader don't understand the central issue of availability. I am always searching for audiobooks, belong to Audible, get them from the public library, rent them from Recorded Books. Nevertheless the human-read audiobooks are a tiny fraction of the library of book available to the Kindle. Particularly for nonfiction works of history and politics human read the available audiobooks are skimpy indeed.
The criticisms of the synthesized voice seem to me a glass half full-glass half empty issue. While the overwhelming number of comments on these blogs disparage the synthesized voices as too robotic to bear, I have been impressed at how human sounding they have become, how large their vocabularies, how few plain errors of pronunciation they make, and the degree to which they can phrase a sentence correctly, inflect a question correctly, etc. When an actor reads they supply the emotional nuance. When you read printed text you supply it yourself. The computer reader is somewhere in the middle. I have "read" maybe 200 books using a computer reader to supplement human read audiobooks. In almost all cases the text was one that no audiobook company offered for sale and probably never will.