Now we're all well aware that Rafa doesn't get as many free points or serve as many aces as the other top players, but is it really because he can't or that he chooses not to?
Believe me, if he could fire down aces like Ivanisevic, he would, and he'd be damned near unstoppable. Truth is, he has one of the worst serving techniques on tour, and the power he does get is almost all from his arm. You really need to learn the correct technique from a young age but Nadal's forte is in his groundstrokes, so those extra hours he spent rallying rather than practicing the serve have made him the player he is today.
It seems, you can't have the PERFECT player with world class groundies and a world class serve. Maybe the chosen one will come along one day though, Federer wasn't far off at his peak.
Nadal has worked on adopting a strategy on serve though instead. For the most part, it works well, especially on clay.