Leosghost - 5:22 pm on Sep 4, 2012 (gmt 0)

Your assumption is erroneous..
Interest based ads are based around the concept of repetitive advertising..

Thus Google's criterium for whether they show an interest ad on your site is not "will it engender a click whilst it is showing on your site" when compared with them choosing to serve a content based ad of equivalent click value..

Google's criterium is "will showing an IBA on any single site, result in a click on that IBA over time in that or consecutive sites that the visitor goes to"..

If G shows content based ads on your site the CTR might be 5 clicks per 100 "shows"..that is 5 clicks for you and 5 for G..

If G shows IBAs on 10 sites and the CTR is 8 per 100 shown overall..That is possibly 1 click for you per site, but 8 clicks for G ..( IBA CTR is higher when taken over time and if the IBA is set up accurately..than CTR on many if not most "content based ads"..especially if the publisher site does not "prepare" the visitor for the ad or get them in a purchasing frame of mind* ( Buckworks will be along, ( I hope ;) to explain in detail why and how advertisers should use IBAs, she has done so before in a past thread at least once that I'm aware of )

If G shows IBAs , they gain, individual webmasters do not..as it becomes matter of chance ( from the point of view of the publisher ) and factors entirely outside of the control of the publisher as to what frame of mind , ( "purchasing" or "repurchasing" or otherwise ) the visitor who sees the IBA is in..

This is why the showing of IBAs is not optional for publishers..G has IBA inventory to move..IBA works for G and advertisers ( but not for individual publishers ) G will not allow publishers to interfere with that revenue stream..

As netmeg says .."publishers are not going to be allowed to drive the bus" ;)..they can, to a degree, choose where they sit, or stand on the bus..or whether they are on or off the bus..but they ain't gonna get to hold the steering the wheel..

*in French we say "mettre l'eau à la bouche" or "donner l'eau à la bouche"..translates not literally ( ie; word for word ) to "make the mouth water"..a well set up publishers site should be "making their mouths water" when they hit the button and click the ad**..or you can think of it like, a well set up publisher's or aff' page or ad, is like foreplay ;) if it isn't any good, you'll get no rewards ;)..Better is best ..

**As should a good affiliate site...and / or a good ad..