No matter what level corporates go to in order to obfuscate details, engineer spin and generally hide all evidence of particular game projects, eventually the shareholders are going to want to see some facts. This appears to be the case with Blizzard's latest annual report to the US Securities and Exchange Commission.
Eagle-eyed fans have noted the following statement contained within this document - a tome so extensive Wirt is currently using a copy to steady his balance; "Blizzard is currently developing new games, including a new expansion pack to the World of Warcraft franchise, Cataclysm, StarCraft II: Wings of Liberty, which will be released with the new and improved Battle.net, and sequels to the Diablo franchise."
As pointed out by Blues, this could be a typo of some description, although this would seem pretty remote. Indeed it seems far more likely that Blizzard are set to adopt the same strategy employed with StarCraft II, namely multiple sequels designed to extend the life of the franchise. Or, at very least, an expansion pack along similar lines as Lord of Destruction for Diablo II, or the extra-canonical Hellfire upgrade for the original Diablo.
IncGamers dared to battle the uber-boss known as the Blizzard PR team, and came away with the following statement; "We appreciate the interest, but we don't have any new announcements to make. For the Diablo franchise, our full focus is on Diablo III."
Keen readers will notice the absence of the word "no" in that sentence.