This has always been known? Capons live longer than intact roosters. Wethers live longer than intact rams. Every farmer knows this.

Yes. The "surprising" part of the article is when the castration is performed.

(So this doesn't end up just another RTFA thread, an interesting factoid: the "bellwether" is the castrated -- and thus relatively docile -- sheep that wears a bell, helping track the flock.)