Apple (NASDAQ:AAPL) has leapfrogged over Hewlett-Packard (NYSE:HPQ) to become the largest U.S. seller of portable personal computers last quarter, because of the popularity of its iPad tablet computer that it debuted last year, according NPD Group’s DisplaySearch. Apple’s 10.2 million portable computer units sold during the fourth quarter accounted for 17% of the market, . . . → Read More: Market Update: Apple (NASDAQ:AAPL), Hewlett-Packard (NYSE:HPQ), Campbell Soup (NYSE:CPB), Progress Energy (NYSE:PGN)