You know actually a lot of businesses do not need the police and can take care of things themselves. In fact some businesses don't want to get police involved at all and just handle it themselves so they don't read about it in the newspaper. If people read about it in the newspaper they won't want to come to that bar or restaraunt, so police don't get involved and they keep it quiet. Many night clubs and bars operate this way. They are very effective at handling most situations themselves with their own bouncers. I totally can see why they don't want firearms in the place. Again many night clubs and bars I been to have signs outside "no firearms" and some have metal detectors. As long as no one is bringing a gun the place they can handle most situations themselves.
I am sure if the restaurant you mentioned in this post absolutely had to call the police they would, but I totally understand their no firearms policy. If you let firearms in a business things can get out of hand easily and it is harder for that business to be able to handle things themselves.