In my experience it's more a matter of separating the fireams from the ammunition in general; which is a big thing at all of the shows I've been at here in the Northeast. There is NO ammunition allowed inside the hall at all. Not for sale or carry. All ammunition sales are required to take place outside of the main hall, generally in a tent in the parking lot.
Unfortunately, since nobody is required to have a permit to attend a show, or even have taken a safety class, this separation of firearms and ammunition makes a lot of sense. Whether it's for sale or carry. The potential for stupid people to do stupid things is high enough that it warrants this sort of measure. I do think it's overkill to some degree, but I'd rather err a little on the side of safety than to see some sort of accident occur. Hell, I get muzzle-swept by idiots looking at guns so often at these events, I have to keep myself from verbally abusing half the morons there.