Certainly, increased sheepishness would tend to promote a smaller standard deviation, other things equal. For the non-statistician guys there, that can be translated to "mediocre performance by the most popular stocks will glom all the sheep together close to the mean".
However, it is not just stocks with concentrated followings--those same stocks need to be neither stellar nor stinkers for that argument to hold. If AYSI was up 40% we'd see a much bigger spread than we do now.
In very non-technical terms, this is called a "cluster flock". :)