I will often instantly move on from items with no reviews, while stay on the page to carefully read reviews otherwise, and often the negative reviews will clearly point out downsides that won't affect me, or at least make me think the item is ok for the price, so I'm not that surprised.

Certain mediocrity is sometimes preferable to the uncertainty of no reviews.

I think it's a case of correlation, not causation: a product gets negative reviews if there are people buying it. Essentially, a product without reviews is a product that people aren't buying (hence, not reviewing).

Also, a negative review might end up being positive for someone else. I have recently been looking at reviews of Sony noise-cancelling earphones, and made sure to read the negative review(s) as well. One reviewer gave it one or two stars because they thought the noise-cancellation functionality was not worth it. Somewhere, though, in his negative review he mentioned that the sound quality is excellent. Having older version noise-cancelling earphones and being happy with them, I assumed he got a faulty pair and decided to buy them anyway. (I actually ended up buying Onkyo earphones, but that because I ended up by their booth at the last IFA, tested the headphones and fell in love)

This is true for me with third party sellers. I've had bad experiences where small third party sellers list products incorrectly on Amazon and I have to go through the process of returning the product. A negative review can provide evidence that users are getting shipped the right product in the right condition.

In these cases, I often don't care whether the user actually likes the product. I just want to know they got the right product in good condition.

Makes sense. A negative review implies that the product was delivered. No reviews calls into question the legitimacy of the seller.

There is an interesting talk by Jason Cohen about honesty in business including Canon's experiment with negative reviews: http://vimeo.com/48549019