"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.