Google is a fierce and capricious God, swift to anger and once angered impossible to placate. A rash of recent law suits speaks to this issue very clearly. The problem is this: Google has long complicated and exhaustive rules for publishers displaying their ads. Those rules allow them to ban any publisher for pretty much any or no reason and once banned that publisher can has no chance of getting paid on the ads it had generated revenue on.
The Poster Child for this problem is Pubshare.com. These guys racked up over a million dollars of Adsense revenue which Google refused to pay because Google claimed that they had breeched their Ts and Cs. Pubshare is suing to get paid. Part of the problem is that Google has allowed various of these publishers to accumulate a very large exposure before shutting them down and refusing to pay. One might think that given the level of attention and automation common at Google they might have some robots tasked to look for just these problems. Google has long since made it more or less impossible to syndicate their actual search ads but AdSense (meager tho it often is) has represented a way for sites of all sizes to generate some revenue in addition to what ever banner inventory they may have.
These kinds of cases are understandably devastating to the businesses involved but of minimal concern to Google because their Ts&Cs essentially grant them all the power they could possibly need. The problem Google has is that the law of the land may not agree with that power and this kind of horrible publicity is likely to make some people with really good traffic to think twice before putting all their revenue eggs in the Google basket. For now the judge involved is letting the case continue it will be interesting to see where it ends up.