I'm sorry, what? I always read Amazon reviews before I buy a product and there are positive comments (for products that deserve them, of course). Sometimes I have to go out of my way to find 2 or 1 star reviews (since I mostly try to order items by best reviewed).
I think I know what you were going for but you're wrong about Negative comments being "the norm". It really depends on the product.
No matter the product, there are always more negative comments than necessary with regard to the product's actual worth. Even if a product has few negatives, that's probably more than it deserves mainly due to people having a very out of the ordinary experience even with a solid product. The actual percentage would be way lower than it evidenced on a review site because happy people are less likely to post a review than unhappy people.