A couple of interesting things involved their studies with animal models. Researchers bred rats over generations to produce low and high aerobic capacity groups. First, when low aerobic capacity rats were fed normal food, they were heavier and less insulin sensitive than the high aerobic capacity rats. When both groups were fed a poor diet, the low capacity rats got worse while there was no effect on the high aerobic capacity rats. This shows the buffering effect of a high aerobic capacity, regardless of diet quality.
Second, when the two groups were given an oral glucose challenge, only the low aerobic capacity group showed increased insulin levels. In effect, the deck was stacked against the low aerobic capacity group given normal carbohydrate feeding.
In humans, the study shows that high aerobic capacity protects against a variety of diseases, including diabetes and heart disease. It is important to note that aerobic capacity was measured in METs (metabolic equivalents) - in other words, peak aerobic capacity, not just low-level endurance.
The authors also make some strong statements regarding the importance of the aerobic metabolism in general. They look at it as the fundmamental mechanism behind all human systems and the complexity of those systems. I'm sure some follow-up research is in the works to further develop this hypothesis.