Wal-Mart, the world’s largest retailer, said Thursday the decision was made as part of its overall merchandising strategy to offer a broad assortment of products at low prices. Amazon has been selling lower-priced tablets at thin — if any — profit margins to boost sales of digital media like books and music from its online store. That makes it less attractive for major retailers to carry Kindles in their stores, particularly as online retailers like Amazon.com become more of a threat for traditional brick-and-mortar stores.