I saw this post [adwords.blogspot.com] in the adwords blog, but I think that the adsense forum might be interested in this post as well.

advertisers who are not providing useful landing pages to our users will have lower Quality Scores that in turn result in higher minimum bid requirements for their keywords. We realize that some minimum bids may be too high to be cost-effective -- indeed, these high minimum bids are our way of motivating advertisers to either improve their landing pages or to simply stop using AdWords for those pages