Because you wouldn’t be buying Kraft Mac and Cheese at a Whole Foods. I’d be surprised if they even sell it.

Also, time. I would rather pay more at Target than wal mart because in my experience it takes longer to check out at Walmart, and god forbid the person paying has a problem with their debit card or coupons or whatever.

And I pay more to shop at Amazon.com so that I don't have to go to Target.

Yeah, can't understand it over here either. All the supermarkets in the UK sell virtually the same products, at least as far as major brands are concerned. Why pay say, £3 for something if the exact same product is available for £1.50 or so in another supermarket down the road?

In the US, most major grocers sell big brand products at roughly the same price. There's variance week-to-week as sales come and go, but if you were to plot the prices of P&G, Kraft, or Nestle products at stores in a specific area, there would be strong overlap.

High-end grocery stores do not tend to sell these brands -- You'll find 0 P&G products at a Whole Foods or Fresh Market. So in that sense, they are selling the same exact products.