We've always had a highly iterative development process, and the unannounced MMO is no exception. We've come to a point where we need to make some large design and technology changes to the game. We're using this opportunity to shift some of our resources to assist with other projects while the core team adapts our technology and tools to accommodate these new changes. Note that we haven't announced any dates for the MMO.
The moral of the story is, essentially, that unless you have information directly from the developers, don't pay too much attention to the rumor mill! As WoW Insider's Matthew Rossi commented yesterday, this is nothing new for Blizzard, with similar actions being taken for Warcraft III. We can only hope that Titan doesn't go the way of Starcraft: Ghost.