Wal-Mart

Low population density in most areas. The few areas in the west with a higher population/population density (i.e. California) also happen to be some of the richer areas in the U.S. (or at least higher income producing). Because of this fewer people in those areas will be willing to buy from a store that boasts low prices like wal-mart. Goods from wal-mart are considered inferior. What that means is that the more income you have the less prone you are to buy them.