The official release date of TES IV: Oblivion is "Early 2006", as stated in the
official FAQ and as clarified also in
Pete's update topic.
It's concievable that the calendar is dated, or that it's marking another event of sorts related to Oblivion. Or that they're simply wrong, like many others are and have been.
The official release date, however, is still "early 2006" (and no longer "Holidays, 2005"). Consider Bethesda
the reliable source