U.S. e-commerce sales somehow rose 53% Y/Y for the week of Dec. 17-21, says comScore - the...

U.S. e-commerce sales somehow rose 53% Y/Y for the week of Dec. 17-21, says comScore - the research firm attributes this surge to free shipping offers, extended promotions, and retailer promises to have items delivered by Christmas. As a result, sales for the full holiday season are now up 16% Y/Y, better than the 13% reported last week, though still slightly below a prior forecast of 17%. Amazon's (NASDAQ:AMZN) Q4 should benefit from the sales boost, but did the company sacrifice margins along the way?