This claim really doesn't say much on its own. There are millions (billions?) of products on Amazon. This would be potentially a lot more damning if they released how many items they searched through to identify those 4,152.
It would also be nice if they provided some data on how prevalent these problems are at other retailers and marketplaces.
There's reason to believe the problem is probably worse at Amazon (automated approval process, historic emphasis on low cost and selection) but how much worse is it?