Aaron Gleeman notes that Jorge de la Rosa could be the Yankees back up plan if they do not sign Cliff Lee. Both throw left-handed. Both showed significant improvement over their career numbers since the start of the 2008 season. Jorge is two years younger than Cliff. De la Rosa would come at a lower cost, and the reason can be seen in the movement of his pitches. Both pitchers see mostly right-handed batters, so the study concentrates on those hitters.
Note that de la Rosa does a good job of mixing up the vertical component of his pitches. He throws pitches (mostly fastballs) that stay up, and pitches with a big drop. Almost all his pitches, however, move toward right-handed batters.
Lee adds two dimensions to his pitch movment. His pitches not only stay up and drop, buy move left and right as well. Lee forces batters to add two more dimensions to their thinking when trying to judge a pitch, and that makes solving the problem of hitting him much more difficult. Lee is Kirk to de la Rosa's Khan.