The horns on all my anvils are too big for opening Eyes on hawks, but I do use them a lot for the other work I do (decorative ironwork)
I have 4 anvils in my collection without horns, two are sawyers anvils, one had the horn broken off during the Civil war, and the other is a large stake anvil designed for nothing but blade work.
Anvil horns can be easily replaced by other simple tooling, but don't forget, the anvil was the first "multi-tool" anyone really had. The added benefit of the horn is, it's usually at just the right height to catch you in the crotch, and keep you from having kids, all without surgery! (well, maybe some surgery, and a blood transfusion, depending on how hard you catch it!)
Tony