OXM podcast (interview starts at 37-minute mark) Howard said, "Being that we are Bethesda, everything gets a bit big. So as of last week, we're over 200 endings. That is not an exaggeration, but it deserves some descriptions."
The clarification is that, like other Fallout games, choices you make in the game will affect aspects of the ending, so that figure is really a combination of many sub-endings. The real question, then, is how many times do you have to beat the game to see every sub-ending?
Howard also confirmed that Fallout 3 is twice the size than anticipated and close to the size of Oblivion. "The game is easily 100 hours," he said. Howard also goes into detail about the dog companion. Fallout 3 is still on track for release this Fall.