My take on it is that the forces on the brain now, in certain sports, are much greater than they were.
When I played hockey, I was an average-size player. Now, I'm a shrimp in comparison with the current crop of hockey players. The forces that they generate are much greater because of their greater weight. They're skating faster than I ever could skate because they have longer legs. What I learned from Pat Bishop is that force is a very important factor in the impact on the brain.
That's another reason they're lasting longer, because they're more serious.