Let it Rupp wrote:
What happens between 100 and 400 meters that causes this big dropoff in quality of times?
I'd suggest that the difference between 100m and 400m is actually greater than between 1500m & 5000m, in terms of the body type they demand. The 100m requires very little endurance - it's basically about getting to top speed and keeping that going as long as you can. The 400m requires a lot more in terms of endurance - there are a lot of people who could probably get through a fast 100m on little training, but the 400m requires serious work.
Also, with the exception of Bolt, the 100m has historically been for medium sized guys, whereas the 400m seems to reward being relatively tall. That's because a lot of the 100m is about how quickly you can start, whereas the 400m is about what your (longer term) top speed is. Big guys often find it hard to get out of the blocks quickly, but make up for it by having a higher top speed. Even Bolt is a relatively slow starter at the 100m - it's usually 50-70m where he destroys everyone.
By contrast, I think the 1500m and 5000m both put similar demands on the body. Although the average speed in the 1500m is quicker than the 5000m, the 1500m guys aren't doing anything like their top 100m sprint speed. A 3:30 1500m works out at 14s per 100m, and I'd almost guarantee that most people who can do 3:30 for 1500 could run sub 12s for 100m (or maybe just over 12s).