It’s unclear why Google starts its own Google AdSense discussion group, as there’s already lots of forums that focus on Google AdSense discussion. A valid speculation is that Google tries to retain ads revenue for AdWords’ ads that related to Google AdSense within Google domain itself, without sharing it with other publishers.
The AdSense Help Group will not be moderated. However, there is Google representative with nickname AdsensePro in the group. Anything posted by AdsensePro, you can be sure that it’s official reply and announcement from Google related to Adsense.
Note: Google AdSense Help Groups which was located at http://groups.google.com/group/adsense-help was been archived and is now available as archive for viewing only. New AdSense support is available at https://productforums.google.com/forum/#!forum/adsense.