I see, maybe you are confused on the Term Free Market.
"A free market is a market in which prices of goods and services are arranged completely by the mutual consent of sellers and buyers, determined generally by the natural law of supply and demand.
Yet if someone skews the defining numbers of the market saying that x number of this demographic of people watch a certain program based on our sampling of 10kish viewers then by definition your market is far from Free being it is having an outside control. The people who produce and write a show have no way to directly exchange with the customer without aide of the Network, the Network deals with the advertisers who use a skewed system of measuring results. So the Television market is a highly controlled one and does not even come close to the definition of a Free Market.
Especially being that the measurement of that exchange is vested in a single entity which controls the sampling numbers. (Why would Nielsen over-report certain demographics if they were seeking to provide an unregulated market being that engaging in such activity immediately invalidates any such premise?)
But the buyers and the sellers are more aware of any potential problems with the Nielson’s numbers than you and I could ever be, the buyers and the sellers both spend serious money supplementing and verifying those numbers, and they agree that the numbers are good enough to determine the dollar value of their exchanges. So clearly by definition the market is free, whether you’re willing to accept the truth of that fact or not.