What's not realized is that the FBI count is artificially defined in a way that far undercounts defensive uses. The usual definition of self-defense with a deadly weapon is use of force immediately necessary in light of a reasonable belief that the perp is likely to inflict death or serious bodily injury.
But the FBI UCR Reporting Handbook at pp. 17-18 uses a completely different definition. Reporting officials are instructed, in the case of use of force by a non-LEO, to include under justifiable homicide only killings "The killing of a felon, during the commission of a felony, by a private citizen."
The illustration given (do NOT list as justifiable a situation where a citizen shoots a fellow attacking him, in a crime of passion, with a broken bottle -- the author must have watched too many 1950s movies about street fights) makes it apparent that the assault itself does not count as "commission of a felony."