The ending of the Kill Bill saga is just another instance of Tarantino’s trademark of toring with audience expectation. QT is a master of that and it shows among other parts, at the final duel scene.
After all the other fight scenes, we expect there to be a prolonged fight between Beatrix and Bill. The whole movie is about getting to that point, about killing Bill, and we expect a kick-ass final battle that surpasses the one’s we have already seen. But QT does not fulfill this expectation. Just as we didn’t see the Deadly Vipers massacring the wedding guests, or Budd going medievil on his boss’ ass - we don’t have a proper final fight scene. Instead, we get a scene full of emotion and character, just like opening scene with the two of them at the wedding chapel. The final scenes, change the emphasis of the Kill Bill saga from revenge to regret.