I found this answer from Ebayer:
Both Burberrys and Burberry are authentic according to the main office. They changed the labeled from Burberrys to Burberry 9 years ago.
In 1999 Burberrys changed their marketing name to Burberry. Most of their items changed too however many accessory items still had the Burberrys name. Also, in 2006, after much public outcry, Burberry closed a main manufacturing plant in London and began producing items in China. The Burberry name was the standard, but Burberrys was still being printed in the liner of some purses and clothing. Currently in Japan their is a line Burberry items that are sold that have the Burberrys name. It is a more affordable line of clothing and accesories.