As Lutz says in his book "Car guys vs. bean counters", that was done to make the Leaf battery last longer. The car industry knows that 80% of trips are under 40 miles, so most of the time, that's enough range. Longer, and they cut in the gasoline engine, so there's no reason to stress the battery life.
I thought for Tesla it's 92% for a standard charge. The Volt is extremely conservative in this regard (Chevy was first out the gate).