Every day, Americans visit chain stores in search of bargains. A world without them might seem implausible. Even as the District of Columbia debates whether to welcome Wal-Mart, Washingtonians can buy Cheerios on special at Safeway and shop at the Liz Claiborne sale at Macy’s. From a Whirlpool dryer to Lady Gaga’s latest recording, the best price on name-brand merchandise is rarely found at independent neighborhood stores.