The word "fanwank" is bullshit, anyway. Any time a show or film tries to explain something that has not yet been explained, we've got angry people screaming about 'fanwank'. That word is an insult, and it's unjustified. Why should plot holes not be explained, or missing scenes in history not ever be depicted?
My pet theory: It will impede their own "fanon" (I hate that word and concept) assumptions so it upsets them.
Sharr