Technology has developed in the last 8 years that allows a lower overhead (lay off staff) without a substantial loss of quality, therefore undamaged ratings.
As technology evolves, there are greater demands on the public's time, leading to an erosion in ratings, but a steady rate card, because it isn't reflecting the lessened ratings ..yet.
Corporations will continue to cut overhead (live staff) as long as automation/satellite programming continues to deliver listeners.
Cash flow will always be time-delayed, i.e. behind the current facts, because stations sell on the ratings of the past.