Baseball has continuously made subtle changes to the ball that better regulate hitting. It seem like season after season they tweak the compression of the ball, the feel of the stitches, or even the humidity the balls are stored at, all to provide more control to either the pitcher or batter for any given year.
At times when viewership is falling, they insert a hotter ball to promote more home runs. When hitting is up they introduce a ball with raised stitching to give pitchers more break on their pitches, or a softer ball that seems to fall out of the air at the warning track. From the bleachers or on TV, only the diehard fans can tell the difference.