I can think of 20 million reasons why you're wrong.
Can you explain the 20 million thing..... is that unique listeners in a hour, day, week, etc,?
Or is it total listeners in a week, many of which have tuned in each day... thus repeat counts
I've looked for rating numbers to see how they actually rate the listeners in radio but can't find anything. I think it is Arbitron that does the ratings...