Oh, I see, so you envision a world in which everyone uses Amazon.com's wallet app. "The masses" may be stupid, but they're not so stupid that they'll use a wallet service that takes far longer than every other wallet service for their transactions to get confirmed.
But as long as it clears before Amazon ships, nobody will be the wiser. And if Amazon is putting that much processing power into the network to save a few measly fees, I still think it's a net loss for Amazon (in our hypothetical).