[Jensson]

A majority of Googles revenue comes from running ads on their own sites. Their third party ad network is a small part of their revenue, so the correct direction is to say that Google is subsidising its third party ad network via their first party ad business.

The effect of antitrust would then be that Google separates the ad service for its own services and third party services, which would force their third party ad service to become more expensive since it can no longer rely so heavily on the draw of all the Google properties.