From a Reader's Perspective.
As a Canadian citizen, I cannot shop on Amazon.com; I must shop at Amazon.ca. Since I usually only buy ebooks, that's not a hardship (all the non-book things that Amazon.com sells, Amazon.ca is slowly, like death crawl slowly, adding, but who has that kinda money??)
Buying an ebook from Amazon.ca is a bit tricky. One, most reviews are posted at Amazon.com, so I have to click a link to get to them. Two, there's no "Look Inside" feature at Amazon.ca, so I have to go to Amazon.com to check if the author did any kind of editing and knows jack about hooks and sentence structure in the way I like (or increasingly, can abide).
So sorting my preferences and attempting to buy and/or download books I might actually like is a bit of an exercise, but the Amazon experience doesn't stop there! No, I get my book, and then Amazon.ca sends me an email a week later asking if I'd like to review it. Why, yes, I would! I would like to review it! Reviews help my fellow authors, after all, and someday I, too, may get reviews.
I click on the link, write a review, sometimes nice, sometimes not (sadly it is a rare thing I find an ebook that truly delights me.) And then Amazon tells me that I am not allowed to post the review. In order to post a review, I need to buy something, once every thirty days. Anything. From Amazon.com. Where I'm not allowed to shop, being Canadian and all. Without a purchase, I cannot post reviews.
So to all my fellow authors wondering why I don't post reviews, good, bad, or indifferent on Amazon, that is why. Amazon hates me. Because I'm Canadian. Or something... (that's a smirk in their logo, innit?)