There's just been another spate of AdSense publishers booted out of the program, not for specific click fraud, but because their "... account has posed a significant risk to Adwords advertiser..." That's GoogleSpeak for MFA, arbitrage, or whatever else Google considers to be a low quality site (no real content except for ads, scraped or heavily duped content, disabling back buttons or any other methods of leaving short of clicking on ads, etc) Is this just a new disabling message or is it for a different kind of site? Some friend of mine buy arbitrage and got banned... He created a blog, put 3-4 articles in it... Is this because he didn't update his website often enough or is it because something wrong with the arbitrage...
Basically they are doing more for the advertisers, and its good, if publishers put themselves in the shoes of an advertiser for a moment and imagine spending 100's or 1000's daily/weekly, imagine how annoyed you would be at your ads being on a 3 page, updated 6 months ago MFA that makes money for the publisher and wastes the advertisers cash. Im guessing that google has a weekly clear up and wipes out a load of them in one go and will continue doing so.
If I were an advertiser, I do not care where my ads show up. I only care whether I got good return from what I spend.
Thats the point though, if your ads show on a site where people click and no one buys, to milk every last penny it can through adsense and encouraging people to click on the ads and waste your money then you would not be happy. Consider conversion ratios for advertisers.