Another General Motors Failure

I have been scratching my head for years as I’ve watched General Motors produce impossible not to ignore advertising. Except for a few rare cases, most of the advertising for Chevrolet, Buick, GMC, Pontiac and Cadillac (OK, listening to Led Zeppelin is good) has felt like it came from a 1957 advertising text book.
An article in Business Week, “A New Spark Plug For Cadillac. Brand-fixer Liz Vanzura aims to do for Caddy what she did for Hummer” discusses the shift of half of Cadillac’s advertising account to the savvy Modernista from old-school Leo Burnett.
I guess that it is good that GM is finally shaking things up. But, here is the part of the article that really blew my mind:
“Like many big companies, GM rotates sales, finance, and even purchasing managers into ad and marketing posts, and those neophytes have looked upon a big ad agency with decades of service to GM as a welcome safety net. Vanzura represents a new breed at GM that LaNeve wants more of: professional marketers confident enough to take risks.”
Please, someone help me understand how a company that wants to succeed has purchasing managers and finance executives running marketing and advertising? I thought GM is in decline because it makes cars we do not want to buy. Now I have an even better prospective on how a great company can set itself up for failure.
Now, I wish that I actually do not see this mistake happening at other companies. What is it with management that they think that just because someone watches TV, opens direct mail and reads ads they are now worthy of running marketing?