By this measure, Maddux owns the top two spots of all time. In 1994, his ERA was 1.56 and the league's was 4.21, a differential of -2.65. In 1995, Maddux's differential was -2.55. In 1968, Carl Yastrzemski led the American League with a batting average of .301. Nominating Maddux should not imply a lack of regard for the great players of the past.
Training is better, nutrition is better, and the players work harder in the off season.
MLB today also draws on a much broader pool of talent than it did 50 years ago, before MLB included the best African American players as well as the best from Latin America and Japan. Because the difference between the star and the average player is less today, it is much more difficult for any player to dominate. I agree with Will. And I think the amazing thing about Maddux is that he does dominate, even in an era when the hitter is king. Four Cy Young awards.