While that's an impressive number, that doesn't even include the players who received Diablo III as part of signing up for the World of Warcraft Annual Pass promotion, which accounts for upwards of 1.2 million players.
On the day of launch, over 4.7 million gamers around the world were poised to play Diablo III, making it the biggest PC-game launch in history. As of the first week of the game's availability, that number had already grown to more than 6.3 million*.
And while 6.3 million is impressive, that number doesn't include players in Korean Internet game rooms, where Diablo III has become the top-played game, achieving a record share of more than 39% as of May 22.†