It's not a matter of winning (sure Poland and Germany have easier opponents), it's the fact that they must win by x number of goals. The USA has no such burden to win by a certain number of goals, just win.
It's still conceivable that the US won't advance even with 6 points, if Italy beats the Czechs, there would be a three-way tie in that case, and most likely the US would be eliminated due to an adverse goal differential, assuming they didn't beat Italy by at least two goals.