For the first time since the game's release in 2004, World of Warcraft: Mists of Pandaria became the first expansion pack that didn't manage to outsell its predecessors on launch day.

According to one analyst, sales are down more than sixty percent when compared to the early sales numbers of the 2010 Cataclysm expansion. During its first twenty-four hours on sale, World of Warcraft: Cataclysm racked up 3.3 million sales between digital downloads and physical sales at traditional brick-and-mortar stores. The previous expansion, 2008's Wrath of the Lich King, earned a similarly impressive 2.8 million copies in its first day of sales, while World of Warcraft's original expansion (The Burning Crusade) managed 2.4 million sales on opening day. So it's a little shocking to hear that Mists of Pandaria only managed to move between 600,000 and 700,000 copies after seventy two hours on the market, even considering that digital downloads haven't been factored in yet.

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Even if Carrett & Co's Brean Murray is correct, and nearly 1 million users were to download the software from Battle.net, it would still only mean 1.6 to 1.7 million in sales. Those numbers would likely be welcomed by most companies, but are unlikely to be viewed favorably by Activision Blizzard. Assuming Murray's digital download predictions are correct, 1.6 to 1.7 million in sales would still be a 30 percent drop from Burning Crusade's launch and just over 50 percent of Cataclysm's release figures.

Of course, these numbers are all relative. World of Warcraft remains the undisputed king of subscription model MMORPGs, and a title has yet to emerge which could truly challenge Activision Blizzard's lock on the massively multiplayer throne. The title is so successful it still accounts for 50 percent of the company's operating income. Mists of Pandaria's sales may have been disappointing, but that's only when compared to prior World of Warcraft expansion releases. Few other studios would shed a tear over nearly a million units sold on day one.

That being said, developers ought to consider readying a new round of challengers. As many reviewers have already pointed out, Mists of Pandaria is beginning to expose WoW's age, and Activision Blizzard is already planning for the future with its "Titan" project.

If subscription numbers continue to drop, could World of Warcraft finally be dethroned after nearly a decade as King of the MMO Hill?

(Update: Official numbers have been released for Mists of Pandaria's first week of sales. Click here to read more)