To some degree, but not to the degree Danielle Steele, Tom Clancy, or Dean Koontz do. At least he doesn't recycle the same story over and over and over again. As far as selling millions of books, he shouldn't be viewed as a poor writer because of this. And he does write what he wants to write and not necessarily what readers want him to write.
Recent examples would be The Girl Who Loved Tom Gordon and Hearts in Atlantis, which certainly were out of the norm from his usual stuff. He wrote a non-fction book about writing called On Writing (obviously knowing it wouldn't be a bestseller). And King took 30 years to write all seven Dark Tower books, despite the bitching and moaning of fans.
King kind of retired after Dark Tower 7 but continues to write for fun, what he wants to write, when he wants to write, no deadlines, and he will only submit works for publishing if he feels they are of good quality. He just published a book about the Red Sox season last year, non-fiction (Maybe some New Englanders will buy it, but I won't). He recently announced he has written a new fiction novel (a crime novel) that he will give to publishers this year, likely in stores next year.
In this respect he quite unusual for a popular writer.