Google makes money by acting as a broker between advertisers and users of Google. Advertisers pay lot of money to Google to show their ads when likely buyers search for keywords in google or use other google services or visit adsense-enabled sites. You are probably right, there is no kind of auditing going to happen about how the money from banned adsense accounts is going to be distributed, and they have a reputation of banning people left and right even when the adsense publishers have done nothing wrong.