Remember the law, and think how many fishermen and other boaters ignore it.... You just have to have PFD's in the watercraft. Only children 12 and under MUST be wearing them. Anyone else chooses whether or not to wear one. In this case, they chose poorly. In my opinion, someone (the operator of the Duck or whoever), should have had the foresight to advise the passengers to don PFD's when the waves starting coming.
There were a lot of other boaters caught out in the waves. Saw a pic of one of the docks near the Kimberling Inn that got torn loose by the winds while boaters were trying to get to shelter. To my knowledge, the Duck was the only tragic incident that occurred.