Robin's
still coming to
Batman: Arkham City, but he's going to be available as a playable character in the challenge mode rather than the main story. So why did Rocksteady decide to let you play as Catwoman instead?
Well,
Dax Ginn talked with OXM and stated that Catwoman represented a contrast to Batman and would offer up a different experience than if you would play Robin. She's a criminal so she'll be doing things and going to areas where Batman wouldn't go, although I don't think there are areas Batman would stay away from.
I do think the decision is the right one as Robin's too similar to Batman and you're going to be spending the majority of the time as him in the game. Having a different character with some different moves and motives should spice up the game a little bit. I can't wait to get my hands on the game.