Many of the nation's retailers are reporting strong sales gains for August.Columbus-based Limited Brands, Target, and Costco are reporting results that beat Wall Street estimates. Limited reports an 8 percent increase. Teen merchant Wet Seal reports a worse-than-expected decline. The figures are based on revenue at stores open at least a year, considered a key indicator of a retailer's health. Consumer spending accounts for 70 percent of U.S. economic activity.