I think US runners have had their minds blown by the huge drop in marathon times over the past few years. Ten years ago, a 2:10 marathoner would be someone you would talk about being in the hunt at Boston or NY. Now, it would just be The track and road circuit are more attractive than marathons for US runners. That is why guys like Heath, Hill, Jager, Rupp and Centro have spent years on the track without even considering the marathon. If it was 10-15 years ago, they would have all taken a shot at the marathon by this point in their careers.
So, the current crop of marathoners coming up are in a way the US "B" team for distance running. Only Curtis and Puskedra have solid track credentials of all the US marathoners with a shot at beating one of the three favorites. Guys like Eggleston, Arciniaga and Pennel pretty much skipped any sort of career on the track.