I think something to realize with some of these slower times is that the best Americans are running lower distances at this point and time. The Americans pursuing the marathon, as in this race, were not top-performing college athletes or world-class at the lower distances (meaning actual contenders in the 1500/5k/10k WC or Olympics).
I'm not saying Galen Rupp will suddenly bust out a 2:06-8 tomorrow but if you're a world-class/elite American runner you're more geared toward the track distances when you're young. You'll try to win in the 1500m, 5k, or 10k - races you've trained for the majority of your life.
As was pointed out before by others, the average age of the East African marathoners is decreasing. I think the talented Kenyans and Ethiopians, though they can run very fast/world class 5k/10k times, are choosing to train for the marathon because they can make more money.
World-class American runners will run the 1500m/5k/10k first and then transition to the marathon later.
Basically, our really good talent is focusing on the shorter distances and lesser talent is focusing on the marathon.