I would think the crew would have been very self critical of the fact that they missed setting the flap. Not having the flaps set for takeoff could lead to a very bad situation. However because of this, Boeing have a very affective take off warning system, that has been described above, and that worked as it should and the crew reacted correctly to it. Why they missed setting the flaps only they will know. Distractions happen for a multitude of reasons. But in the end a safe takeoff was achieved. Lets not bag them too much.