2004 saw the sharpest drop in deaths in around 60 years - down almost 50,000 from 2003. The research team for "Death: Preliminary Data for 2004" from the National Center for Health Statistics, suspects that the drop is due to decreases in deaths from heart disease, stroke, and cancer - the leading killers. It may also have to do with 2004 having a mild flu season.
Gardner, Amanda. April 19, 2006. 'U.S. Death Rates Drop Dramatically'.