People place Adsense on their websites and then earn a percentage of the AdWords money you are spending with Google. Whenever money is involved, so is greed and deception.
That is the exact reason why some people choose not to advertise on Google's network of content sites.
Personally I do both. I have some campaigns that I advertise on the search only, and others I advertise anywhere possible.
If you are thinking about advertising to the content network, I would run a comparison test. In that test, bid the same amount for the same keywords and then check your ROI and conversion ratio.
If you are converting 40% less, but the clicks cost 50% less, you are still making money. If the clicks convert the same, you can possibly either get more clicks, or pay less per click and use your entire daily and monthly budget.
Google AdWords is the only PPC provider that allows you to advertise anywhere but the search engine. To change this feature in AdWords, click on a campaign, then click on "Edit Campaign Settings" and you'll see, on the right side, how you can adjust the content versus search settings. You can also see the screen shot in this post.
