User blog comment:Master Sima Yi/Assassinews 03-03-'13 — Assassin's Creed IV: Black Flag trailer and screenshots/@comment-4360293-20130306031537/@comment-4740457-20130306074357

"Because the game is so radically different from the one that came before it. It’s not just about having a new setting and a new hero, although that helps. It’s about the scope, the open-world gameplay being so different from the previous game. The game is just a completely new, fresh beast of its own--it deserved its own number."-Ubisoft