DSO says they're using the "latest drivers" and then provides a screenshot of the 331.65's -- Nvidia released the 331.82 WHQL drivers yesterday, which among other things, are the "game-ready drivers for Assassin's Creed IV."
Obviously they performed the analysis before the 331.82's were released, which begs the question as to why they did a performance review before Nvidia released the proper drivers for the game?
You can't draw proper conclusions about Ubisoft's work when you're on drivers that pre-date the game. The same drivers also improve BF4 performance by up to 18%, and Crysis 3 by up to 26%. It's probably safe to say that performance in AC4 is going to be much better than their test indicates, and will continue to improve with future driver updates.
That's the nature of PC gaming. It's not entirely on the developers; sometimes Nvidia and AMD's driver teams end up being tasked with supporting dozens of new, major titles in the Fall and game-ready drivers fail to be released before the game, and then over the following months performance increases considerably. Future patches to the game will probably help as well.
It'd be nice if everything worked perfectly smoothly on day one, but that's almost never the case (especially in PC gaming, but also increasingly in console gaming).