"if sarsen stone is so hard that slight wear would not erode in 3000 years than it is too hard to wear from wooden rollers in the first place."
Wear and erosion are different things. Sarsen is not immune to wear (see the polisher thread above) and 1,000 years of use would have left marks. Surprisingly a softer substance can wear a harder as it can pick up and retain grit and other abrasive substances. Mill stones, even the best from the Marne Valley in France need to be dressed and they don't touch one another.
exactly what sorts of marks would you expect to find from long wooden rollers that spaned the width of the sarsen sapstones. yes, a small wheel traveling constantly along the center might make a grove but a roller that completely covered the stone would leave no specific marks. this test can be conducted on our model mill by spreading very fine sand on the sarsen ring then allow the mill to turn for a bit.....the result is a very smooth even covering of sand along the entire ring.