I don't think they realize quite how big of a barrier [a download] is for many people.
I agree. I believe that WalMart's "solution" is the "Shop and Go" functionality in their app. You scan your purchases as you put them in your basket, and then go to a special register. Your "cart" is sent to the register, and you complete the purchase normally (using a credit card).
If so, this isn't the same as NFC payment. It's something completely different, and WalMart is trying to explain its way out of this. The real issue is they have already spent a lot of money putting in custom EMV terminals, that don't support NFC.