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.