In fact, professional heavyweight boxers usually develop parkinson's whereas that's virtually a nonexistent problem in welterweight and lower.
This is actually why I much prefer watching lower weight MMA fights to the bigger guys. The fights tend to go on longer and are more dynamic. With the bigger guys, one solid punch to the head and it's often game over.
Interesting stats. I'm not sure it completely explains the higher weight divisions though, since if you look at the rate at which the heavier fighters get tired and start lowering their guard, it's much higher than in the lower weight divisions, leaving them more susceptible to the KO/TKO.
Can confirm. Getting hit by a 200+ pounder sucks. Getting hit by a 130lber makes you wonder if they're even trying.