He wrote about himself and writing in a book titled On Writing:

http://en.wikipedia.org/wiki/On_Writing

So I guess if he makes statements that sound like writing advice he probably means them as writing advice.

(None of which is really a counter to something as absolute as 'ultimate authority', but maybe you could elaborate a little)

I've read On Writing, though not recently. The strong impression I have is that his advice was intended as just that -- advice, rather than binding pronouncements.

That is, King in On Writing seems essentially to be saying "Here's what worked for me. Maybe it will work for you, too," rather than trying to be Moses on the flank of Mount Sinai.

And, for any wordsmith, much of his advice has value! Certainly there's no doubt of that. On the other hand, King is a writer of horror fiction, and I am not. This, at the very least, suggests that not all of his advice will be applicable to my purpose, a consideration which seemed absent from the comment originating this thread.

If you assume King is clear and intentional in his writing (which of course he is), there is a lot of nuance available in "you have to hunt for".

Writing covers a topic large enough to encompass the act of programming, news articles, and poetry. Assuming the author intended it in the widest possible sense and expected it to apply to every situation does a disservice to both them and yourself.