It has been confirmed by Microsoft that Bungie is in fact working on another Halo game.  So the canceled announcement could very well have been Halo 4 for the Xbox 360.  Any Bungie game would have probably stolen the spot light from the games coming out this fall like Fable 2, Gears of War 2 or Fallout 3.  It definitely would have taken away from the Square Enix announcement as well.  

Now if I was Bungie and was told the announcement was canned but the Microsoft head of Xbox blurted out the game was a Halo game, well I'd be pissed.  You have to know there are tons of Bungie fans waiting to see what possible new IP  that Bungie is working on.  To find out second hand that it is a Halo game really loses it's steam.  Sure another Halo would be awesome, maybe one told from the point of view of the other Spartans (yes, there is more than one).  The odds are this game will not be ready till 2009 or 2010 since it normally takes Bungie about 3 years to develop a game.

Source:
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