Why not for cloth?

http://psgraphics.blogspot.com/2007/05/my-top-utility-papers.html
Prof. Shirley mentioned in his blog that his "An Anisotropic Phong BRDF Model", JGT00 is not good for cloth.
Does anyone know what he means by that?
Is that an issue in expression or on implementation?

Shirley先生の方法は、どうして布には適さないのか？表現上の問題、それとも実装上の問題？