If you thought there would be a gradual transition on TV, you read the wrong sources. There was a gradual building out of the digital TV stations that had to be complete by July 2006 (after one of the first delays). But the analog cut off date had been set for a while. I am forgetting now, but it seems the original cut off for analog was for 2005 or so and that was set from nearly the begining if not the beginning. Trip remembers these type of facts better than I.
With FM there never has been nor even proposed an analog cut off. Personally until Digital Radio (because it's dang sure not
HD) becomes really
HD and a LOT more robust, I hope analog isn't ever proposed to turn off.
Plus where people own a TV or so, they probably own half a dozen FM radios. One in each car, main stereo, kitchen, bedroom clock radios, etc, etc.
I think while IBOC is here to stay for a few years to come, the FM transition has not really even started.
Another good reason is power allowed. A station can only transmit 1% of it's total power as digital. For a 100KW full power, this is 1KW, which has about 2/3 to 3/4 the range of the analog signal. Which can cover a town.
But then take the myriad of 6KW LPs. That would mean they could only run 60 watts on digital covering a few square miles around them. Why bother? I am not even sure the rules if LP stations can run digital. Another Trip the
FCC expert question.