Many Amazon product pages are the de-facto location for product data in a variety of verticals. When was the last time you read a great book and sent someone a

Many Amazon product pages are the de-facto location for product data in a variety of verticals. When was the last time you read a great book and sent someone a Borders/BN link? If that page page becomes the default home for that product, posting a review at Amazon becomes natural. This also leads to weakness in other areas, and I'd argue that for product categories where Amazon is not the natural choice, the review quality isn't fantastic (e.g. outdoor gear, etc.) If the goal of the review is to inform as many people as possible about your product experience, Amazon is a natural outlet.