Its hard to tell what is selling. Many sellers, for example make up kit deals with bodies and multiple lenses, even Canon has a kit and non kit version. Amazon does not add up all the 50 or 100 different versions to give a total, so the information is not really accurate.
I also believe that Big dollar camera equipment buyers do not buy from Amazon, most of them have learned the hard way. Amazon seems to have pretty well given up on selling lenses, at least the last time I checked, only a very few were sold by Amazon. They likely got bit by returns from inexperienced photographers.
I've bought quite a bit from Amazon, and really the only issue I've had was with the 5D2 Kit I recently purchased. Out of the box, the 5D2 had an issue where the shutter had sprayed lubricant onto the sensor. (At least that's what I was told.) So I sent that back. Actually, returns can only be processed for items up to a certain value. Since the kit was too expensive, I had to re-purchase a new kit, return the first one, and wait for a refund.
The second 5D2 (which I still have) came out of the box with a sensor full of dust and debris, which I thought was odd. Maybe that's common, but I hadn't experienced a new camera with a dirty sensor.
I've purchased lenses through Amazon to take advantage of Prime, so far with success.
I'm interested to know: how has Amazon burned you?