Usually lines 3 and 4 are asked to fill certain roles, generally defensive roles, while the top 2 do the scoring. Seems that the US lines 3 and 4 have been asked to play a sit on the bench role. As are the dmen after the top 4 (and I'm not sure who the 5, 6, and 7 dmen are). There's got to be depth in the US team, if they don't have it, they should have picked it.
The OT goal by Germany (Chorney letting the Germany forward get between him and the goal) and EJ's screw-ups in the third period today may well have been from total fatigue from logging so much ice time. You picked them, Rolston, best give all of them them a role and let them play.