This paper argues (following Gould, 2003) that the disappearance of the .400 hitter in major league baseball is due, not to a decrease in ability at the top end of the talent distribution, but to better methods of screening out players at the low end of the distribution. The argument is related to the economic literature on minimum quality standards in markets with imperfect information.
Miceli, Thomas J., "Minimum Quality Standards in Baseball and the Paradoxical Disappearance of the .400 Hitter" (2005). Economics Working Papers. Paper 200515.