Here is the new details Rocksteddy revealed:
"you can also play as Robin, and NO! he doesn’t look and seem like the movie versions. Robin will have new arsenals of gadget’s and weapons to use and also a new combat style. Robin is a lot more agile than Batman and I hope we see this being true in the game. Robin also has Explosive Vision, which allows the player to figure out the best way to avoid or use explosives."
It sounds like to me that Robin will be a playable character regardless you preorder or not. This is great news I loved Arkham Asylum but this one seems like its going to be way better. As for the Robin changes I dont mind them the movie versions of Robin sucked anyways.