When they talk about an artist's need to learn storytelling, this is what they mean.

If you want a good, no nonsense tutorial about comic book storytelling, then take a look at this Saturday Evening Post cover from three years before I was born. Three panels that tell a complete and engaging story, all without the intrusion of any text or dialogue.

I think this shows more compellingly than just about any other example I could imagine how it is the artist's job (and burden, and glory) to tell the bulk of the story in any given comic book.

Just starting out drawing comic books, or trying to break in to the business? Then study these three panels. Click on the image to enlarge it and give it a good and proper going over. It won't take a long time to plumb the depths of these three panels. It's all there with remarkable clarity and simplicity.

Drawing ability and storytelling ability are the two pillars on which a comic artist's career are constructed -- period (unless we are talking about work ethic, but that is a whole 'nother discussion). Drawing ability is a difficult skill set to master. Storytelling ability is more about how you see things and can imagine translating them to the page. This one example (from an artist I sadly cannot identify) pictured here is a master class in that subject. Enjoy.