free throw trends over the years

My brother sent me a link to the New York Times Freakonomics blog (you know, the one with the logo of an apple that tastes like an orange, which is kind of odd because bananas might soon taste like apples) that has some new insight into an earlier New York Times article about how free throw shooting has a roughly constant, non-improving percentage over time. In both the NBA and NCAA, overall free throw percentages have remained fairly constant for several decades. Freakonomics adds that while overall percentages remain constant, the very best from each NBA season (20 players with the top free-throw percentages) have an upward trend. As is mentioned, this inevitably is reaching a plateau since you can’t shooter higher than 100%. 

Both these trends are interesting and I think deserve a little more research. If the overall percentage is staying the same and the best are getting better does that mean the worst are getting worse? Or could this be a product of the NBA growing from 9 teams in 1960s to 30 today (more players could push the extremes out while keeping the same mean)? Or could this be a problem with redistributing the number of free throw attempts to the worse free throw shooters? I don’t know if anyone in the 60s instituted the hack-a-Wilt strategy (probably not since it doesn’t sound as good as hack-a-Shaq), but it’s clear today that intentionally fouling a bad free throw shooter is a commonly used tactic in certain situations. Also, if defenses are getting smarter or more informed they would probably be less likely to foul Ray Allen on the open break than if it were Rajon Rondo. 

Provided I could get the free throw statistics for every player in every NBA season since the 1950s, I would look at the change in distribution of free throw attempts as well as looking at the average if giving equal weight to each player (with some minimum requirement of free throw attempts). Giving each player equal weight would create a form of standardizing the NBA seasons regardless of what type of free throw shooters are shooting the most.