You are right about Peter Jackson regarding LOTR fanfics, but not so J.K. Rowling. In fact, Rowling was so belligerent about a tribute reference work entitled "The Harry Potter Lexicon" which was published with a claim of fair use, that she sued the publishers. She won the action, in a finding in New York that the Lexicon used too much of Rowling's work in its reference; and she was awarded a grand total of $6,750 in statutory damages. The year she won that action she made $300 million. Petty? You bet.
Woe be unto anyone who writes a Harry Potter fanfic.
I am fully aware of the Potter Lexicon and the legal action. In my opinion, that wasn't fanfic - that was creating a book that Rowling very conceivably would have written herself, or had others write. AS such it was providing a product that people otherwise would have been willing to actually pay her for. I can see how she thought that was stepping too hard on her financial toes.
Since several of my online friends have been into Harry Potter, I have dabbled a bit in reading fansites (never posting, or writing fanfics, since I have not myself been very gripped by the HP universe). Rowling has given interviews directly and exclusively to fan sites, sites which host fan fiction - interviews in which she has deliberately fuelled the flames of the "shipper wars" that have raged in those very fictions, and so forth - there is no doubt she is aware of and has actively made use of the fandom *and* (indirectly) fanfiction and has tacitly considered it beneficial to maintain the huge and continuing interest for her series.
Same with Anne Rice's works - she will sue anyone, at any time, under any circumstances, for daring to put about a fanfic about any of her works.
Anne Rice is quite the anomaly among fantasy/SF writers, though - there is one other female Fantasy author known for a similar strict stance. (Can't recall her name now, but she was signing books at Forbidden Planet in London one time I was there, and I thought it tempting to have asked her about that, but I didn't dare....)
And Annie Proulx would also go into that category of aggressive pursuers of fanfic writers. Her lawyers went after me and at least three authors I know of with cease and desist letters. I dealt with it (I don't have $100,000 to prove adequate transformative fair use, nor did I want to) by withdrawing all fanfic pages from the Web, and subsequently modified all of the stories to remove any and all references to Brokeback or its characters. As far as I know, Anne Rice and Annie Proulx are among the top rank of aggressive pursuers of fanfic writers.
The C&D letters from Proulx's publishers came after they (correctly or incorrectly) believed that money was being made or would be made from those fics, as far as I know. When Jenna started selling her bound and illustrated cine I was very worried she might be crossing a line long before the C&D arrived.
The difference between Proulx and other fandom biggies is that she writes "literature" and they are mostly SF/Fantasy writers - there's a tradition for fanfic and fandom activities in that latter arena that the lovers of "War and Peace" and "The Brothers Karamazov" do not match (yet). I don't think Proulx and her publishers were at all expecting the fandom activities, and they proved awkward and incompetent at handling them IMO. Of course, I won't deny Proulx the right to bitch out all and any persons writing Brokeback fanfic. That's obviously her prerogative and her opinion. Mine as her reader happens to differ. We're both entitled to our views.
I stand by my previous posts - the internet has created new and much more accessible reader and consumer opportunities of digesting and enjoying and interpreting literature of any kind, and the publishers and authors had better get round to finding constructive means of building on that instead of chasing enthusiastic and imaginative readers with scowls and threats and lawyers. Their financial interests in the long run will be more at stake if they continue down that antagonistic path. I am pretty sure Anne Rice has lost out big time, both in revenue, interest and goodwill, for denying her readership the opportunity to write about Louis and Lestat till their hearts' content and till their fingers bled.