One way to see if the top earners' earnings have been affected is to view the HubPages Sucess stories page, take note of who they are, then go visit their profiles and see what they have recently being saying by looking at their recent activity - which may show that they've been active in the forums, complaining (or not complaining) about their recent earnings, or may show that they've recently written a hub about the topic.
My HubPages Ad Program earnings for April 2012 were $14 - the most I have yet made on HubPages in one month.