This is true but most shoppers tend to shop before buying. They don't always buy on the first page they land on no matter how well it is written. Placing adsense on the bottom of the page is not putting it in their face to leave. I know that the topic can be debated over and over and having it on our website is just my opinion of a way to re-coup the cost of bringing the customer to the site. Besides with getting a nice check to cash every month it makes you feel that if you didn't get the sale you at least re-couped something. It's better than them hitting the back arrow and searching again and the big G gets it all. As far as the percentage goes who knows it's still better than nothing.