He uses stories - including a letter he received from a soldier in Iraq. The stories are personal and back up his simple point, thus they are concrete and credible. Emotion is really the driving factor in this talk, you can hear it in his voice. He is passionate about this and this passion shows.
His unexpected is subtle. He starts with a joke (an inside joke that references the previous talk which must have been really good) which is unexpected. He also looks at the talk from a different point of view. Many times we search hard for an "in your face" unexpected. This can be difficult and over time people will expect that you are going to do this, so it is not so unexpected. (That's the problem with Purple Cows). So Dr. Greene takes another approach he looks at his topic from another point of view. To be sure he must have been given a topic and some speaking points, but by modifying these points he is able to fulfill the simple messages that the topics was meant to cover with something unexpected to wake people up. Some people may think - wait he did not use his speaking points exactly, that must mean he is not that great of a speaker. To that we say - you be the judge. Take note however, this was during the Aspen Festival, many people must have been tired, must have been feeling sleepy - even I was when I watched it. At the end of the talk most eyes must have been awake.