Excluding the 800 (which is sort of a distance race), here's the USA's totals for races of 1500 and further at Olympics and Worlds since WWII...
|Year||Golds||Medals||Top Eights||Top Twelves|
A number of things should jump out at you when you look at this data. First, the USA hasn't ever been particularly good at distance running, except for the baby boomers. They did very well in the 60s, and the trailing end of that generation did decently through the 70s. But it lags remarkably behind literally every other part of the US program save the walks.
Second, something happened in 2007. That something was more than just Bernard Lagat; while he won all the medals, the depth of the US team picked up quite a bit as well. 2008 appears to be an anomaly for the USA, a one-off in futility, in all events, not just distance.
Lagat says his US citizenship made the rest of the USA's milers and 5k runners get better. There have been other immigrants, though, such as Sydney Maree in the 80s and Mark Plaatjes in the 90s, and neither had such an impact. It looks like American distance running is getting better at every level all at the same time. One of the most encouraging parts of the Berlin results was how many of those top runners were young -- all but Lagat are in their 20s.
The decrease-then-increase syndrome is also evident on the women's side, but not nearly so marked in either direction.