One way to look at this is that it's part of the CEO's overall compensation-and-benefits package. Instead of paying the money to the CEO and having her (or him)

One way to look at this is that it's part of the CEO's overall compensation-and-benefits package. Instead of paying the money to the CEO and having her (or him) purchase a security service, the company can purchase it directly. And a large company like Apple probably just has part of their security staff protect him. Losing a CEO is extremely disruptive to any company, and so this can also be seen as a business expense, similar to insurance protecting the company's headquarters building.