There are what 1 billion internet users on the world, let's say 1%clicked on the ad and bought the product... (you do the math)
Ofcourse numbers are bigger, and it's not just the google ad, you have to pay so that your page appears first, now just think how much is it payed for the most searched word on the net?

You are right, but i keep my opinion that it's overextimated :D

The share price mostly accounts for future growth, but during the internet bubble so many internet companies were overrated that the market crashed, NASDAQ still isn't on those levels...