In light of that recent article about computer-generated prose being in many cases indistinguishable from human-written, I'd say those fake reviews are likely written by a computer. Notice that they're mostly of the form "I didn't think I'd be interested in [TOPIC] but [TITLE] was really interesting and really helped me learn about [TOPIC]."
That's an interesting thought. I'm pretty sure I could write up a nice grammar to chunk out "interesting" reviews of books. Instead of whining about my book getting buried by fake reviews, maybe I should chuck it and cache in on said reviews!
That they don't have an efficient algorithm for this sounds more like they don't really care and never bothered with it.