Blizzard says Microsoft is, Blizzard says Microsoft isn't. Some stories are completely predictable.
With the Xbox 360 over three years old, it's as likely as not that Microsoft's already broached the subject of its Xbox 360 followup act (in one form or another) with whoever it's dubbed worthy. But that's about as prescient on my part as suggesting Toyota's presently rendering concept sketches of its 2012-2013 midsize lineup, i.e. "it's the common sense, stupid."