Despite US having a number of good scoring opportunities the shots still came under pressure--excellent marking defense by Japan. The final goal, by Japan, in stoppage time, was the nicest goal of the game. Also don't forget the blown offside call that would have given Japan a breakaway.
Possibly most important was that the Japanese coach had his team loose, smiling, light, going into the shootout. US was as tight and nervous as could be--maybe coaching psychology at the end was the real difference--but in IMO shootouts aren't much better than a coin toss, game should go on with a golden goal after the 30 minutes OT, shootouts just suck.