Just to further your point, we are in a thread about Kubrick who did numerous book adaptations including Lolita, Dr. Strangelove, The Shining, and Clockwork Orange and this is just off the top of my head. Tons of directors adapt novels. Bringing the story to the screen is the skill.
As an aside, 2001 is an interesting case as it was produced concurrently with the novel. It's clearly not an adaptation, but I wouldn't say it's clearly original material either.
