In less than 24 hours since the rumor spread, Blizzard has issued a statement to clarify that the story F13.net reported is just a false rumor. Here is the official word, straight from the horse's mouth
"No, that rumor is not true in regard to Blizzard. We believe that the rumor circulating about this subject is based on a misinterpretation of information provided to industry analysts. We do not currently have any MMO development plans beyond the upcoming expansion for World of Warcraft, and furthermore, we don't have any intentions to focus on only one genre or platform with our future games."