Perhaps Ubisoft wants the Beowulf game to have that authenticate touch of Hollywood. Maybe the publisher has a thing for Sir Anthony Hopkins.
Or - and this is a long shot - Sir Anthony actually plays a character in Beowulf, and it'd be a bit silly if the game based on the film had someone else doing the voice.
Whatever the motivation, Sir Anthony Hopkins (Alexander, Red Dragon) will provide the vocals for King Hrothgar, while Ray Winstone (The Departed, King Arthur) will dispense the grunty, yet effervescent, tones of Beowulf.
Oh, did anyone else noticed that one of the plot keywords for Beowulf on IMDB is "Stabbed in the arm"? Just goes to show you can make a movie about anything.