Truly, one Google hand doesn't know what the other is doing.
EzineArticles and AskTheBuilder have both been hit by the Farmer update (so Google Search evidently hates them) but these same sites are also featured on the Adsense site as success stories (so evidently team Adsense loves them - MFA / spam / thin content = success).
Who could not argue that the indiscriminate granting of Adsense accounts to any and all sites is really the biggest factor in the proliferation of spam sites on the web.
What team Adsense does is just like what happens with other areas of business (hand gun manufacturers, banking/credit industries, fast food, etc...). They make a legal product, without any concern or sharing any responsibility about how it is used or how it affects society as a whole.
Google search may try to be "Do no evil." The Adsense side is simply American business as usual. Screw everyone, we just care about hauling in the money.