Sergio Muñoz Sarmiento takes up the question I posed yesterday:
"I would add that it wouldn't necessarily have to be a 'crass commercial artist,' but could simply be a corporation searching for advertising material, such as Apple did with Marclay's video. It cuts both ways. If artists want carta blanca to do as they wish with others' property, why shouldn't the converse also hold true? ... Transformative should cut both ways. Why should Mannie Garcia be granted less protection, or considered less of an artist, than Fairey?"
(The Apple-Marclay incident is discussed in the article mentioned here.)