your question isnt very clear; but if you are asking how/why they block/ban accounts, i think it pretty much boils down to if you break their rules and they catch you, they block your site/ban your account.. if that's not what you were asking, please clarify..
https://www.google.com/adsense/support/bin/answer.py?hl=en&answer=48182 Check it out. Hope you find answer.
you can found them policy from google website , they offer the updates they add and the new policy ! https://www.google.com/adsense/support/bin/topic.py?topic=8423