Blizzard weighs in on the rumors.
As a rumor of Diablo III will come first than StarCraft II spread by internet, Blizzard has confirmed to IGN that the StarCraft II is on track for a 2009 release.
The details are as below:
Which will come first, Diablo III or StarCraft II? According to Battleforums.com, it#DY#s the former. The gaming web site reportedly received an anonymous tip from a Blizzard employee that read, "[Starcraft 2] is still being worked on, but only by a minuscule amount of people compared to what [Blizzard] put on the Diablo 3 team." As a result, the site reports that Diablo III will release before StarCraft II. If true, this comes as substantial news considering Diablo III was revealed at the company#DY#s 2008 Worldwide Invitational on June 28, 13 months after StarCraft II#DY#s announcement at the same event last year.
IGN contacted Blizzard for clarification on the matter, and here is what a company representative had to say:
"We#DY#re very pleased with the progress of development on both StarCraft II and Diablo III. In fact, we#DY#re looking forward to sharing news about both games at next month#DY#s BlizzCon event. We don#DY#t currently have any release dates to share, but development is proceeding at full speed on both games."
While we don#DY#t know specific release dates for either title, Blizzard recently confirmed that StarCraft II is on track for a 2009 release.
Read More Here.
Resource: IGN

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