There are certainly expenses incurred by the publisher that have nothing to do with the physical articles.

It seems like the marginal cost of the "last step" cost is still a very significant component, though. High-touch sales channels, handling returns (consignment sales), and co-promotion expenses all seem tightly coupled to that "last step" and sales of physical articles.

It's been a while since I've looked at it but, basically, the cost of the physical article is a smaller slice of the pie than many think. There was a lot of discussion about this when e-books first got big and weren't that much cheaper than mass market or trade paperbacks. As I recall, the number was around $2/copy.