It really does bug me that the Giant Bombsquad and even the guys at Rebel FM are so put off by the fact that you can't play the game past the official ending. I can totally understand why Obsidian would think it's not worth the time and effort to make a DLC pack a la Broken Steel for the reasons that there's a fuckton more variables that the expansion would have to factor in with a game engine that's infamous for its blunders in causality.
And, they do tell you before the end-game sequence in 300 foot tall neon letters "THIS IS THE ENDING OF THE GAME." Is it really that big of an issue to save before that point and not play that sequence until all the DLC packs come out? For god's sake, what excuse is that to not free-roam in that time?
Yeah, it's a minor bummer you can't see the consequences of your actions at Hoover Dam, but to do a DLC pack about that would mean rendering half of the sidequests you may not have already completed and maybe even completely wiping them all out.