When I do staples like that I raise small burrs on the lower legs to keep it in place. Once hammered in you would have to destroy the horn to get them out, I tried once. And yes the staple is nothing more than a "Keeper" to hold the strap in place or set it up for Right or Left carry. Depending on the placement it can move the way the horn is carried, in toward the body or twisted out a bit.
I think the Pic is of a modern strap attached wrong on an old horn. Which looks to me to be a Bottle Turned Tip Lancaster Pa. horn.
Tim