Marketing is pretty similar to finance, it is a staff function which does not contribute directly to revenue or to product development or even to design. Marketeers main job is to tell a story about a product and make sure that the plot, characters and arc of story are coherent. How is this like Finance? Simply Finance has a similar function in terms of what it delivers to a business. A controlling function to ensure that price is right and other functions are run as efficiently as possible. They allocate capital between different functions of a business.
At a macro level Ad Agencies and Financial Institutions perform similar functions for businesses, and as has happened with all aspects of business in the last decade, the services being provided have become unmoored for any real value addition. This piece in the FT is ostensibly about rise of online media, but reality is that the go-go years have ended and advertising will not command the premiums that it once did.