My reasoning being that they suck away a lot of revenue from Google. Rather than Clicking to each of the products in turn via AdWords, you click once and Google loses all that revenue.
These companies take revenue away from Google .. I do not think there is any question about that. The only question is whether or not Google will see it as an issue.
Actually, they can (and most likely do) bid less if the CTR rates are high enough.
What does the individual bid rate matter if the higher CTR on review sites leads to a higher overall revenue for Google? A click by someone who wants to a read a review is worth more than a non-click by somone who does not want to go directly to an order form, no?
When you go to a review site, you're a lot less likely to click back and slowly click through all of the products on Google. Rather, you click on all the ads listed on the review site.
I was thinking about setting up some review sites, but it occurs to me that there is a downside risk of having google/overture shut me out. Not huge, but its there. Less downside risk to other things.