If you had asked me five years ago if I'd be regularly ordering from walmart.com instead of amazon.com, I'd have thought it unlikely. But here I am -- I don't have to worry about counterfeits as long as it's sold & shipped by Walmart, and I can get same-day delivery (usually within an hour or two) for the cost of a tip. Their inventory is different (many more consumer staples, at better prices; many fewer random long-tail products), but it's replaced maybe 1/4 of my Amazon purchases. I also order from target.com once in a while; I never ever used to.
Amazon has not lost, but it is definitely losing its unique edge.