I agree that Short Stories are different from Novels. It's like the difference between an episode of a T.V. show and a Movie. Even if the T.V. program is part of a larger whole as far as story arc you still have to fit the basic elements of character, plot, problem, conflict, and resolution of the story being told in that episode within a period of 45 minutes instead of the 90 minutes or more of a full length movie. Movies like Novels can have subplots and multiple story arcs while there isn't as much room to do that in a single episode of a series or in a single short story. Novels let you explore at a slower pace than with the short story too I think. While both jump right into the story from page one it's a more hurried pace in a short story than in a novel length story, and not every story can be told in both formats I don't think either. I re-read 'Zen' a short story by Jerome Bixby last night and I don't know how he could have made it into a Novel.
That doesn't mean he couldn't have done it, only that I can't see how he could have stretched the basic story any longer than he did.