Helen Robson Walton, widow of Wal-Mart founder Sam Walton, died Thursday evening at her home, the company said in a news release. She was 87. Walton was surrounded by family members when she died of natural causes, the news release said. "We are so proud of our mother and the life she led," said Rob Walton, eldest son of Sam and Helen Walton and chairman of Wal-Mart Stores Inc. "She devoted much of her life to helping others, and to improving the quality of life in Northwest Arkansas. "Today, my brother and sister, and the entire Walton and Robson families...