As athletes get bigger, stronger, faster, and more well-trained and records repeatedly fall in other sports, the percentage of free throws made in college and NBA games has largely stayed the same.
The consistency of free-throw percentages stands out when contrasted with field-goal shooting over all. In men's college basketball, field-goal percentage was below 40 percent until 1960, then climbed steadily to 48.1 in 1984, still the highest on record. The long-range 3-point shot was introduced in 1986, and the overall shooting percentage has settled in at about 44 percent.
I've said it before and I'll say it again: it's amazing that with so much at stake in the NBA game (wins, money, championships, glory), there are still players whose FT% is in the 50-60% range over the course of a season...for a shot that undefended and never changes! I wonder how the putting percentages have changed over the years in golf (if they even keep such statistics). The Times' Room for Debate blog has a related discussion on unbreakable sports records.