Sorry to nitpick with an anecdote, but the closest Walmart to me is over 60 minutes away and I don't live in a small town, just one that rejects/blocks "big box" stores aggressively. Walmart certainly has a lot of stores but not everyone has one just around the corner (thankfully)
The bottom line is that Walmart's physical presence in the U.S. absolutely dwarfs that of Amazon... outside of NYC and a couple of mega-urban metropolises, who see Walmart as more "evil" than Amazon because they're in the mindset of still fighting the previous war.
But still, 60 minutes means same day delivery without too much hazzle. An advantage Amazon doesn't have. Disadvantage is the considerably higher fix costs of Walmart and the like.
Dropshopping could, theoretically at least in my opinion, provide that geographic reach without adding additional fix costs for a player like Amazon.
EDIT: Typo