Hey, I don't think I've ever seen a thread about this before!
First of all, Obsidian doesn't make these types of decisions, Bethesda Softworks (publisher) does. Obsidian didn't even know whether or not they were going to be asked by Bethesda to make DLC at all until close to NV's release.
Second, how do we know Microsoft didn't bankroll development of the release? If they did they sort of own it in a way, right?