I think the difference is that in that case Amazon controls the entire chain. They have the batteries manufactured and plan stock themselves. For market place items on Amazon (which are now most items) someone else just rents a bin in their warehouse, ships stuff to it and gives Amazon a description to show on their website. Amazon in that case is more like Airbnb for goods or a more automated eBay.

It would be interesting to see counterfeit numbers for items sold by Amazon itself vs by someone else on Amazon. Anecdotally I've never had an issue with stuff sold by Amazon itself and steer away from our vendors if possible.