[Nasrudith]

My guess is they might fill a supermarket niche more in denser urban areas. I don't know first hand but it cluld make sense.

I heard accounts of ironically Whole Foods which is referred to as "whole paycheck" in other areas being the cheap option in some areas. I would guess traffic vs stock would also influence prices in non-obvious ways. With perishables, more expensive real estate, high traffic, and customers more likely to buy everything by foot they may be less of a speciality niche in urban areas than suburbs.