Saw this interesting bit from bakadesuyo. The point is that if you have cars, you can drive around and make price comparisons. Comparisons make consumers more aware of price differences, thereby increasing the price competition.
This research undertakes a carefully designed and detailed empirical study to gain insights into (1) the extent of price differentials between wealthy and poor neighborhoods; (2) what induces such differentials, especially the nature and intensity of competitive environments, including mass merchandisers like Wal‐Mart; and (3) their relative impacts. It finds a price differential of about 10%–15% for everyday items. Even after controlling for store size and competition, prices are found to be 2%–5% higher in poor areas. It also finds that it is not the poverty level per se but access to cars that acts as a key determinant of consumers’ price search patterns. (Source: bakadesuyo)