The FDA is concerned about how certain pet diets are being sold.

Truth be told, this is gratifying- many prescription diets are really only intended for patients with the condition for which the diet is a treatment, and may not be healthy for other pets! By the same token, it's a bit misleading for food companies to compare their non-prescription diet for a given condition against a clinically-tested prescription diet for the same condition. 

Via, "FDA Releases Guide on Pet Food Diets Intended to Treat Diseases."