An analyst report says Amazon.com (AMZN) and Apple (AAPL) continue to grab market share from major U.S. consumer electronics stores. J.P. Morgan analyst Christopher Horvers said in a Wednesday investor note that Amazon and Apple are growing at the expense of big box retailers like Sears (SHLD) and RadioShack (RSH). His analysis is based on a 2011 estimate of the Top 100 consumer electronics retailers issued by the Consumer Electronics Association