Well, one thing is to hit aces, but I think that Roddick gets a lot more service winners. Fed put his racquet on a lot of balls, but he also missed a lot of those. Roddick's kick serve isn't meant to be an ace, but rather something that will keep him the advantage in the point. Honestly, aces aren't that important if you win the point one way or another. The fact remains that his serve cannot be attacked easily. It can be returned, but not attacked. I mean that on a consistent basis.
The more important stat is first serve points won, and not aces. I never liked Roddick's game, but I have to give him credit for having the best serve in the game right now.