As is true with every holiday season, the key to relative success at any large retailer is the extent to which it can gain and hold market share. It is hard to imagine the worst-off retailers will increase their pieces of what is still a modest-sized pie. That means it could be a hard holiday for the likes of J.C. Penney Co. Inc. (NYSE: JCP) and Sears Holdings Corp. (NASDAQ: SHLD). For them, the 4% increase in overall spending this Christmas season will fall short of what they need.