I was just reading some statistics from
this page relating to gun prevalence, safety training and reported gun violence.
Paraphrasing, in 1998 there were 9755 firearm homicides reported to the FBI. 40% of those were the result of an argument, where a gun happened to be within reach. Furthermore, there were 17424 firearm suicides in 1998. That breaks the statistics up into appropriate categories rather than citing "over 25000 firearm deaths in a given year."
For the first point, a gunshot wound is generally more lethal in nature than a knife wound, however I think it's likely that in arguments between the type of people who would shoot each other, if a knife was handy instead of a gun it would be used to settle the issue. I think the real issue at hand is that the immediate lethality of a gunshot wound skews perception of the violence of the crime. The only difference between a large caliber gunshot wound and a knife wound is the energy involved.