Given the amount of visitors that it could attract from the village tourist load, I'm not surprised the landowners want exact locations kept quiet. Though the cup marked stone may underwhelm more people than it would inspire, especially after they'd been wowed by the bigness of Avebury, the polisher offers a sense of intimate frisson that's quite a powerful counterpoint to the massive impersonality of the more gigantic stuff.
I know Avebury is very big and clever an all, but Fyfield Down is the best spot in Wilts as far as I'm concerned :)