Maybe I misinterpreted the article too, because an "excess of overcaution" sounds a lot like blame shifting to me, in this case from the rating agencies onto the investors who believed the ratings. The argument implies that because investors were "overcautious", and only willing to buy AAA rated securities, the rating agencies were therefore compelled to rate things AAA they otherwise would/should not have. At any rate, it seems that rating agencies should be rating things accurately regardless of how cautious investors are.