True, Mr. Wizard - about the level of arms carried by 99.9% of CITY DWELLING Tejanos. However, for the country boys, most are carrying at least a 30 aught in their rifle racks. Whether they would dare bring it with them to a concert in Big Cities (Midland, Odessa, Lubbock, hell yes ... the bigger cities have gone to crap) - is another question. And as you're well aware, even a moderate marksman can hit even an elevated target at only 340 yards with a 30-aught-six. It would only take a couple of those good ole boys to be within sprinting distance to their pickups.
A hand gun - duck and cover is definitely the better option. Las Vegas venue - not sure any of those pick-ups would have been around - too many city slickers with stickey fingers.
Bottom line - Yeah - the outcome would almost certainly have been the same here. Odessa- maybe not.