Here is a guide from a publisher trade group on the implementation of ad block detectors under gdpr.

It says that listing the use in your ToS is a defensible strategy but could have some risk. If the organization wants to further limit risk, they can add a consent banner, consent wall, or both.

My guess is Google is the risk accepting type on this issue and it’s willing to litigate to argue that its ToS is sufficient or the way they implement it differs from cookies. Either way, they could completely make this go away by asking a consent for ad delivery to their cookie notice.