This is against the AdSense Policies, so there are three possibilities here.
- Weblogs is blatantly violating the policy
- Weblogs is a premium publisher and has negotiated the right to put more than 3 ads per page, or
- Weblogs is participating in some kind of beta test for Google
Jason Calacanis, who runs Weblogs Inc, has this to say:
I can not comment on this beyond on the statement below, but I can assure you that we are not breaking any rules with Google and we are in constant contact with the fine folks over at Google.
Very official statement from Jason: If you would like information on Google Adsense running on our sites please contact Google’s press or Adsense departments. I can assure you we are not violating any terms with them. I can not discuss the issue beyond on that.
Given this statement and the fact that Weblogs, Inc. is making around 1 million dollars a year from AdSense and has a lot to use, I highly doubt that they are violating their terms of agreement. It remains to be seen if this is something available only to premium publishers or a beta test. I hope its the latter.
Also see: ProBlogger