As far as I know ratings download from amazon works fine. If you have a particular book(s) for which it does not work, then feel free to post its ASIN/amazon URL and I will take a look.
As for review counts, that's not something I am interested in. But you can easily write a plugin that does it.
Oh and note that calibre does not use the amazon API to get data. APIs cannot be used in general in non-web software since they would require every user to get their own API key.
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