A few months ago, Bethesda disappointed a large portion of the community when it announced that TES IV:Oblivion was not going to make it as a launch title and delayed the game until March 2006, saying that more time was needed for polish.
Spanish site players4players claims there is more to it, as a confidential source told them that the real reason was a little bit more interesting. Oblivion had already been finished, but upon arrival of the official Xbox 360 dev kits, they realized the machine was more powerful than originally anticipated. Bethesda then decided to delay the game for optimization, especially of the graphics.