@Wilso,
I felt a bit bad for the US runners as well, but then again, getting the technical aspects of the skill right are just as necessary as the strength aspects.
I felt like many of the runners (not just US) were sloppy in a number of technical areas. Not only did a few teams drop the baton in the relays, but a few also disqualified themselves by stepping on the lane-lines during various races.
And then on the other end of the spectrum there's Jamaica, an island which seems to grow and train the fastest humans on the planet somehow.