No, no, no, no. I think you misunderstood my post (and to some extent, so did
@muCephi) - but if that misunderstanding arose from the way I phrased things, then mea culpa.
I wasn't in any way implying that the studio had any power to determine what fair use was or wasn't. I was merely using an analogy that, because they have set their guidelines up in a way that is roughly analogous to some of the analyses that would be made under a fair use defense, their allowing people to make films that comply with the guidelines is functionally equivalent to the studio letting fans know that they would consider fan works that meant the guidelines to be a fair use for which the studio would not seek damages for infringement. Similarly, the way they set up the guidelines, they can point to violations of the guidelines as evidence against a fair use argument – for the reasons outlined in my post.
But I never meant to imply that the studio was itself creating a fair use defense (not only would they have no power to do so, but someone who complied with the guidelines who was sued by the studio would have something much better than a fair use defense – in effect an estoppel (and possibly breach of contract) claim against the studio for going back on its promise to not sue a fan film that met the guidelines.).
And, yes, there are good arguments for a binding enforceable contract there, under any number of theories of contract formation – including the separate theories of an agreement with consideration (studio made an offer and the filmmaker gave consideration by changing its plans to comply with the guidelines) and promissory estoppel (studio made a promise on which the fan film relied to his detriment by changing his plans to comply with the guidelines on the belief that this would avoid a lawsuit.)
M