Without producing examples or statistical analysis I think that there were holed stones placed upright around monuments. Maybe just one of them. What the holes' symbolic purpose was we will never know but they certainly weren't for tethering horses. Or sheep. For long. When the puritan Saxons came along, with their big hammers and superstitious beliefs, these already weakened stones were easiest to fragment. Like cupmarks the purpose of the piercing may have had more to do with the making than the object itself, particularly if it was subsequently buried.
Sonicator at full blast - I now leave it running when I go out on errands. If it's working properly the water warms up. Now I know the hair rings are ancient they have taken on a precious aura.