Let's take one of those examples, then.
With "The Sentinel," as I recall, the story began with someone going to check on a strange artifact, & ended just after it broadcast a tight message. That's it; the overall denouement was, "Now we're waiting to see what happens." Correct?
That forms a piece of 2001, true enough... but it was in only an inappropriate &/or dishonest sense "expanded" from a short story to a novel (a series, in fact) -- making such a claim is like saying that a typical novel is made from strung-together standalone pieces, which rather is unusual if not rare. Matter of fact, I'm fair certain that the POV is changed, the setting & occurence drastically chopped, & that it becomes little more than a passing anecdote to set up the main body.
The novel was not an "expansion" of the story's plot. By definition, a short story (to abuse Dorothy Parker) runs the gamut from A to B, or perhaps more appropriately from E to F, while the novel must manage to make a much larger range.
I think it'd be amusing to watch someone try to write, say, Cryptonomicon in 5,500 words or less.
Could it be chopped down? or could a scene or subplot be pried loose? could all but three or four of the characters be eliminated? Certainly.
But that would no longer be the source novel. Just a pried-loose chunk.
I'm reading a nonfiction book by an agent who mentions selling a novel on the basis of a 150-page presentation. I have my doubts he could have done so with less than 10K words
Therefore, to claim that a short story is a novel minus the adverbs -- or that a novel is a short story with entire chapters describing the wallpaper -- is nonsense.