It is different. This is talking about Amazon Marketplace sellers. It would be more similar to if Walmart set up a flea market with tents and stuff in its parking lot and let anyone rent a booth and sell whatever they wanted. Walmart would also provide a centralized cash register at the end of the parking lot where people could pay for the items they got from the individual sellers. Walmart would then settle up with the sellers at the end of the day for the sales they rang up for them, while keeping a cut to cover the cost of the transaction and logistics for setting up the tents and keeping security guards on site.

This would be an equivalent analogy. Does THAT seem different than going into Walmart and buying from inside Walmart?