How Google has changed showing ads over the years

If you are a AdSense publisher then you probably already know that there are so many policies about how you should place an ad code on your site. And one of them is "Publishers should avoid website layouts in which the ads push content below the fold. These layouts make it hard for users to distinguish between the content and ads."


Well, I'm really curious to know that Google tells us how we should place the (farther away from the content) so that people don't click it without knowing that it's not the part of the content. And at the same time they are going from full visibility to stealth. Why is that?  I think they have found out that if the ads are  visible too much people don't click on it, so they earning less money. And that's why they are going so stealth that it's almost hard to notice the "ad" sign.

On one website I read that it is good because now advertisers can get more visits. Well, then my question would be what if other publisher do the same (go almost invisible like Google)? That will serve the same purpose I guess. OK I understand that if someone just click on an ad and don't really like destination (advertiser's) page, he might lose money. That's why advertisers don't like this kind of clicks. That's right, but Google don't charge them if someone clicks on an ad and then don't stay on the destination page for some time anyway. So the question still remains, If Google can go stealth then why not other publishers?

Once upon a time advertisers would like to die just to get a little space on some website and now they getting free hits (those hits that people don't stay on their sites for about 30 seconds or so) and publishers have to provide free space for them. What a time to living in! :(