PlayStation snagged exclusive DLC for both Watch Dogs and Assassin's Creed 4: Black Flag. But, "exclusive" typically means "timed exclusive" in this business, and that happens to be the case here too.
The 60 minutes of new gameplay promised for both games are exclusive to PlayStation platforms for 6 months only, a new video released by PlayStation reveals. That means you'll likely be able to play as Aveline on Xbox and PC just by being a little bit more patient.
Of course, Ubisoft could choose not to release the content on other platforms at all. For example, the PS3-exclusive Benedict Arnold missions for Assassin's Creed 3 never made it to any other platform.