All I can tell you is I was being pretty careful, as I always am in my online transactions, and I feel I was both misled and that Amazon did not provide value to the transaction.
I am absolutely certain each item I put in my shopping cart said it was "in stock", yet days after the purchase, I received emails from the various providers telling me the real story. I am also certain that even though I tried hard to find out prior to the purchase, it was not possible to see the breakdown in shipping costs. Only seeing one shipping cost line item is one reason some might believe its all being bundled together from a big amazon warehouse somewhere. Especially with widespread business articles like the OP educating the world that's what Amazon has become. Otherwise, why not show me 4 different shipping charges, maybe I want to send one priority and the others not.
I also filled out feedback on these purchases after I received the shipments to state what my complaints were about the shopping experience, but never heard back from anyone. This part of course, doesn't surprise me. Simply pointing out that if I were to do something like this again, I may as well buy direct from the real supplier so that if I did have a problem, I wouldn't be complaining through a middleman.