No, it's the way the track is created that has more or less dust... The tracks with a lot of dust actually use the dirt surface in the track, and the ones that don't have as much dust use the grass surface with a 'dirt' texture applied to it. The result is a slippery surface that looks like dirt, but doesn't make any dust. Then they alternate between a dirt surface and a grass surface to make the dust show up every once in a while.
