Head Bolts?

I just pulled the head off of my 258 yesterday evening to get a broke head bolt out of the block, lucked out, it came out without having to drill and use an ease-out, but I heard or read awhile back that on the 258 when you do a head set that you need to replace the entire set of head bolts. I ain't never done that on anything else I've ever rebuilt or replaced the head gasket on. By the way, the broke bolt was at a waterport location. And what may have caused the bolt to break after it was torqed down and checked again after the first hundred or so miles? Stress or just a weak bolt? It was approx. 2 years ago when I replaced the cam and lifters and timing chain and gears. Any opinions? Thanks.