I was talking about this subject with some RL friends over dinner last week, and one of them made a similar point to your "a": she thinks that book authors should be able to say "no fic" and have that position be respected, because they created the characters themselves. But since characters are mostly created collaboratively in other forms of media, no one has as strong a claim on them, which means that fic of those characters is always okay in her eyes. It's a nuance I hadn't really thought of before she brought it up.

The same-media thing is also interesting. If you read the comments on the GRRM posts, you might have noticed that he is absolutely fine with unlicensed fanart -- actively encourages it, is happy to have people send it to him. He even has a page for it on his website. Changed media is less of a threat? But then, how far do you have to go? I had a conversation with rabbitprint about this yesterday and he raised that point: if fanart is okay, what about a fan comic? Or an illustrated story? Where's the line between storytelling and art?

And I agree that, consciously or not, that insecurity certainly plays a role for at least some authors.