"If a visual artist can appropriate for whatever reason, under the guise that any form of appropriation is, per se, fair use, why can’t a corporation do the same?"

Sergio Muñoz Sarmiento has some more thoughts on appropriation and fair use -- and it's always great when he and Alfred Steiner get into it in the comments.  I think the real value in Sergio's shoe-on-the-other-foot examples is that they point up a problem with the emphasis on "different purpose" in the fair use analysis.  That is, imagine a corporation uses an artist's work in a major ad campaign to sell their widgets.  Couldn't they argue that their use had a completely different purpose (selling widgets) than the artist's ... and thus was transformative ... and thus fair use?