There have been three editions of Assassin's Creed for PC. Not a one of them released at the same time as the console versions' launch. The closest Ubisoft came was with Revelations, which landed on PC two weeks after it did for Xbox 360 and PS3.
Though Ubisoft told Eurogamer that the PC release date for Assassin's Creed III is still "to be announced," word had it all versions would hit shelves or virtual stores the same day, October 30. Eurogamer on Thursday reported that it will be delayed nearly a month — to November 23 in Europe (which would mean November 20 in the US). Eurogamer cited a "publishing source" and provided a promotional image showing the disparity in release dates.
Joystiq took the bullet and asked Ubisoft what was up in order to receive the obligatory "We do not comment on rumour or speculation," which is sort of a weird reply to this particular matter.
Assassin's Creed 3 PC Delayed [Eurogamer]