Weeeell...I kinda have a problem with author comments past a certain point.
Sometimes they are quit interesting, I have to admit. But mostly they are kind of cheating. If your text doesn't address the points your comment does...what is the purpose? Like, why should I care if Dumbledore was gay? Cool for him, maybe makes the background a bit more tragic. But doesn't change anything.
Pluy there is the strong and real possibility of an author not understanding his own work and commenting things that make it 'worse'. We've seen it countless times in Film with Indiana Jones IV and the edits and cuts to E.T. and Star Wars and everything Georgd Lucas ever touched basically. Or when Silent Hill 2 got rereleased and they decided to cut the fog away.
Text comments run the same risk.
The risk offilling important 'Leerstellen' or vacancies in the text with something unfitting, unfinished.
From a more philosophical perspective: It is simply manipulative. An artwork is not the belonging of the author when it is published and consumed by the public. It is part of a free and open cultural exchange like any other. Author comments nudge the reader - who before could apply himself freely in his analysis - in a certain direction of interpretation. Very nice of Bradbury to tell me about the evil of TV and how it makes me dumb, shame I get more and a bit more open minded kicks out of reading Fahrenhsit 451 as anti-censorship.