According to the FAQ on Gamefaqs (PVD disclaims responsibility for game spoilers behind the link), Assassin's Creed II consists of levels called "Sequence 1-11" followed by "Sequence 14". What happened to Sequences 12 and 13? The devs claim to have run out of time to finish them before the game's launch, but will be releasing them as paid downloadable addons. Sequence 12 will cost you $4 and Sequence 13 will set you back $5 on top of the $60 MSRP of the game.
Joystiq's glass half full take on this incident is that additional fees for downloadable content is "saving" content that otherwise would never have seen release (in this case, too small to be marketed as a sequel but probably not directly relevant to the plot of the third game in the series). This view has some merit, at least until Bobby Kotick at Acti-Blizzard and the paymasters at EA realize that they can shave a month off of every game's release date to ensure that there will be unfinished work to put in the DLC.
More interestingly, this type of move could potentially insert a greater level of accountability into single player games. For better or worse, the majority of an MMORPG's revenue comes from recurring fees. When players up and quit en masse, the developers almost certainly notice (though there might be a limited amount they can do about it when the core complaint is that the game needed another year in development to meet market standards for content and polish).
By contrast, pre-DLC console gamers have already paid the developer every cent they're going to pay for a game before they've even opened the disc. Perhaps the publisher has a limited interest in protecting their brand name from association with "shovelware", but such measures are aimed at customer satisfaction for the NEXT installment of the game (which might be years away). With DLC, console publishers have at least some limited interest in not having the game suck so badly that players won't pay for the add-ons.
Don't get me wrong, it's a limited silver lining to a business model that will encourage companies to cut more and more from the base game to save more and more for paid DLC. Unfortunately, it doesn't look like DLC is going anywhere, so I guess we'll take our silver linings where we can find them.