Earlier quoted context omitted.
Agreed, but Amazon as a retail operation is so well run with such excellent customer service it's hard to imagine Walmart outcompeting them.
Walmart is cheaper. Significantly cheaper. You don't have to pay $100-$300 per year plus Amazon's typical 10-20% price premium* in exchange for "free" 2-day shipping. If you live in the right place you can pick up the goods same-day from Walmart, maybe even on your commute, so for some people it's more convenient too. * The usual caveat about everything varying with geography applies here too, I'm sure.
When I need something in a few days (or later), I'll order it from Amazon when I think about it. If I need something "now" or today, I'll just drive to the store and go get it. I, personally, don't really see the point of the "in-store pickup" -- why order it online if I have to go there to get it anyways?