Bungie’s Curtis Creamer explains why in an interview with Jostiq: “”Well, that was something that we didn’t really think we could do for ODST because traditionally all of our DLC has been about competitive multiplayer. That’s something that we had the systems in place for. But, since Firefight is more based on the co-operative campaign mode, that was a technology that we hadn’t built up to a point where we could add DLC to the game. It would have been too much of an investment to make that happen.”

No DLC for you, then.