This service is provided by Blizzard for people who convince their friends who quit to subscribe to World of Warcraft once more. Previously this feature just offered 7 days of free game time but now there are massive benefits to re-join World of Warcraft for ex-players - see below:
|Now that's incentive to get your friend back and for your friend to come back.|
So why have Blizzard given this the crazy buffs it's received? simple. Cataclysm haemorrhaged subscribers, somewhere around the 2 million mark I believe, and I think rather than trying to promote the game to a new audience and attract newer players Blizzard want the people back who used to put a nice steady stream of income into their pockets.
Maybe one day I'll go back to playing but until some of the stuff I quit for gets sorted I'll probably stay away.