Yah, it's easy enough to see where the chain rubs in there as it streches and wears out... would definitely be quieter if some of that material was ground out in advance of the wear.
but then again, it kinda wears itself in to fit... kinda like my crummy ole china tennis shoes. I think they fit ok when I 1st got em, on sale, of course! :-)
now they go on my feets...