From the brief email release:
Warner Bros. Interactive Entertainment and Rocksteady Studios are releasing the PC version of Batman: Arkham City in November. The Xbox 360 and PS3 versions of the game are confirmed to be final and will be available beginning October 18 in North America, October 19 in Australia, and October 21 in Europe and other global territories.
We are still waiting on word if this delay also includes the OnLive version of Batman: Arkham City and will update you with more details.
Despite the sad news, for PC Players, you can feast your eyes on the latest screenshots and pray November gets here soon.