Guided missile launchers are weapons systems, because the projectile and the launcher each are a component of a complete system which requires significant technology. This is in contrast to a firearm, which has all of the technology in the gun and not the ammunition (for the most part) or more simply a knife or sword.
I suppose I'd say: well, no, a gun's ammunition does something significant, but also even if that disambiguation were necessary in a particular circumstance, this article is not that.
