Not quite Dobbsy. First Strike is supposed to represent the skill, speed, surprise etc of the attacker
where that is exceptional.
The question whether this 'ability' should be applied to the weapon or the person wielding the weapon is more debatable, and is down to the mechanics of how the designer sees things happening.
- The Warp spiders ability to suddenly appear (short range warp 'hop') makes their attack devastatingly fast and their ranged weapon allows them to shoot at many opponents, so they have two 'first strike' attacks.
- OTOH while the Banshee mask's howl stupifies opponents who are then dispatched with swords, those out of sword-range have to be shot at with pistols etc hence the second (weaker) FF attack. (The same is true for Rough Riders lance which is good for Hand-to-hand fights, but not for attacking targets more than a few yards away)