The Joker will be available at launch as a free downloadable item on PSN, but will only be playable in the Challenge Maps.
Looks like the PlayStation Home ad just went up a bit earlier than the press release is all.
Read on through the break.
April 23, 2009 - Eidos Interactive and Warner Bros. announced today that the Joker will be a playable character in the upcoming title Batman: Arkham Asylum -- but only on the PlayStation 3. Joker will be available at the game's launch as a free downloadable item on the PlayStation Store. The press release notes that he will only be available for use in the Challenge Maps, so don't expect a massive single-player campaign associated with the legendary villain.
Arkham Asylum is already showing quite a bit of promise, sporting an intensely dark look and action-oriented gameplay. The Batman title is scheduled for a launch this coming June.