Amazon.com Inc. and other web retailers sold more products than ever this holiday season, boosted by early promotions and investments in delivery systems that helped avoid the widespread shipping snags of last year. Online shopping is on pace to rise 16 percent to $61 billion for the November to December period, according to researcher ComScore Inc., with retailers benefiting from lower unemployment rates, higher consumer confidence and a decline in oil prices that has left shoppers with more to spend on gifts.