Amazon top 10 means almost nothing, as it takes in total lifetime sales as well, which is why very old cards are in that list.
Surely nobody thinks an 8400GS is in the top ten cards sold today.
If it wasn't for integrated graphics, I'm not even sure I would be surprised by the 8400GS in Newegg's results. Just go to Video Cards without filters and search by price, and what's the first one that comes up? 8400GS.