I feel you are completely overlooking all of the costs the business incurs. The cost of premises, printing costs, image licensing, insurance, marketing budget etc etc.
What I did was to divide the total revenue by the number of employees. Then if we make a reasonable guess for average loaded labour rate, say 70K GBP (which I think is probably generous for London) that still leaves us 70K per employee for external costs and various operating costs that are not included in the loaded labour rate. That seems quite high to me. Like I said, I'm not in the publishing business, but even when I worked on shrink wrapped software, I would consider that level to be bleeding money. I could easily be wrong. It would be interesting to hear from someone in publishing.