There are weapons in martial arts but generally speaking the definition of it is not used correctly.
It means war art, so if you want to put it that way is shooting someone a martial art? There are of course more traditional weapons but when it comes to what is commonly practiced it is the unarmed stuff.
That is what I have seen anyway, I see a lot more people training unarmed fighting vs training with a guan dao or a bo.
With regard to guns and martial arts, the Japanese samurai included the firearm into their martial traditions because they saw the value:
Are you going to claim that what they do is not a martial art?
Personally I spend more of my time training with a weapon in my hand than without one, and yes I believe what I do qualifies as a martial art. Just because something is common it does not exclude the uncommon. And as I said earlier in this thread I would fully include the training of a fighter pilot to be a martial art as would an infantryman learning to fight his M4. These are clearly modern martial arts, you don't need belts and titles to make something into a "martial art."