Cell phones need scores of towers and fiber running to towers in order to connect to a telephone network. You have a network of them. Disrupting either the physical towers or the cabling that connects them incapacitates that part of the network. Worse yet, the more towers drop, the higher the network congestion gets (which can further jam whatever nodes are still up and available).
Radio has a gigantic broadcast tower (or maybe some repeaters too), that blasts electromagnetic waves across a large region, and, so long as you have power and your tower is intact, you can reach every radio in your listening area.
People will adapt. The car radio was not designed as a safety device, nor does it serve as a particularly good one. It takes on that function somewhat by default, and occasionally does OK, but it's not nearly as important as he makes it out to be, and I doubt that wide-scale removal will have any noticeable impact here. To the extent that it's needed for mass communication, other techniques will be found. The mass text messages sent for Sandy are probably a good model there.
As far as the cost/benefit analysis, I imagine the radio costs in the neighborhood of $5-10 per car compared to not having one. I'd guess that the major expense is the cabling and routing for the antenna, rather than the actual receiver electronics. This is not a lot, but if people don't care, they might as well save the money. It makes more sense when you realize that there are literally a thousand ways to spend $5 to improve a car, but if you did them all, you'd end up with a car that cost $5,000 more.
I would not have thought to bring a stand alone radio in the car that i was borrowing from a family member on that drive. Even in the modern era, it's not hard to believe that someone might have forgotten their charging cable for their phone and allowed it to run down, or a whole myriad list of reasons why a phone may be operating.
The business model is fucked for a pile of reasons, but when we're talking about reaching large numbers of people in a relatively fault tolerant way, there is no competition to broadcast.
A panel of spokescritters from the automotive industry have said that the decision to remove radios from cars has been made and is being rolled out.
He thinks that this is a disaster for the radio industry, and also has ramifications for public safety vis-รก-vis broadcast infrastructures superior accessibility when compared to wired technologies such as cell phone towers and wired phone lines (citing Katrina and Sandy).
I'm sympathetic to the issue of public safety as there are a whole pile of circumstances where Americans may be unprepared with their own radio where it is useful to be able to assume that they can tune in for broadcasts.
The the south is afflicted with hurricanes, the midwest and north east get hit by blizzards, the south west by wild fires. Some of these events are sudden in onset as well as unpredictable in nature.
The weird part here is that we're not even talking about removing the stereo system but just the radio components. The cost/benefit analysis on the inclusion of a radio receiver must have been really freaking weird.