Interesting at a time when radio stations are fighting to maintain their declining TSL.
Nielsen says, "For the 2008-2009 TV season, the amount of television watched reached an all-time high as Americans spent four hours and 49 minutes a day on average in front of the TV, up four minutes from last year and up 20% from 10 years ago. The average household watched eight hours and 21 minutes a day on average, also at an all-time high".
Certainly there are many differences between radio and TV. One of the biggest being the expanding channel line up on cable and satellite which expanded the programming choices 24/7. I also believe the DVR has played a large role and has fueled the expanding viewing patterns buy sucking people into watching more episodes in less time as the can skip the spots.
The bottom line for radio can be summarized in three words: content, engagement, digital. Program entertainment or information worth listening to, entice your users to participate, and use the available digital tools to provide your unique content on multiple levels.