Players who currently own a standard Battle Chest account (which includes both vanilla WoW and The Burning Crusade) need Wrath of the Lich King to gain access to level 70+ content and to upgrade to the current expansion, Cataclysm. A fully upgraded account will also be necessary to install Mists of Pandaria when it is released in the near future.
Since Newegg is a U.S. vendor, it's most likely this sale will only be good for those of you who want to play on North American and Oceanic servers. Sorry, Europe!
Update: It looks like Newegg has sold out of copies of Wrath of the Lich King now.