While Google monetizes its core web properties such as google, gmail, and youtube via a closed advertising system. That doesn't mean the worth of the company is

While Google monetizes its core web properties such as google, gmail, and youtube via a closed advertising system. That doesn't mean the worth of the company is held in AdWords. If Google decided to shutter AdWords and use a third party the third party would still need to pay billions per year for exclusivity. However, Google does leverage their ad business into non-google properties via vertical integration eg. I can buy ads on CNN via AdWords but I can't buy ads on Google search from DataXu or other DSPs.