Concert ticket prices are directly related to the cost of hiring a particular artist, with the profit margin and overhead for the concert organizer (such as the rent of the concert hall, hiring people to sell tickets and gorillas to keep order, etc). What the artist gets must include not only what the actual musicians pocket personally but also any background singers, transferring their equipment, any special effects they need and all the other jazz, like their personal manager's wages. So, there are actually two overheads at play all the time, in addition to two profit margins.
Or like the small text on the site said: "As for an artist's cut of the live revenues, generally speaking, they are paid about half of a show's gross. However, their share must cover their booking agent and manager's commissions, production costs, tour crew salaries, and travel expenses, so the actual artist may or may not pocket considerable cash."
So, the graph showed both the overheads and the local organizer's profit combined (on the left, blue) and then the pure artist's earnings (on the right, white). That's how I understood it.