A crowd can accidentally DDoS a cell phone network. They can't DDoS a radio station.
With radio - regarding natural disasters - you typically have at most one tower per frequency. Often networks will combine their broadcasts onto one tower, aka one point of failure. There's nothing special that keeps a natural disaster from taking that tower out, versus a cell tower.
The counter argument is that cell towers tend to be highly distributed and numerous - even in a bad scenario, drive 5 minutes and you'll probably get another cell tower, and then another, and then another (partially true for radio, but you're going to jump stations doing that, and the Internet will remain up even if you can't access it at one specific tower, ie cnn.com remains up in an earthquake or blizzard).
Most radio stations are small to medium operations, even those owned by Clear Channel (they operate locally, mostly on their own budget, and have local equipment). So regardless of if eg Clear Channel owns the station in question, if you pack enough ice onto its tower, the hardware on it is going to be damaged, ditto for wind. For mom & pop stations, of which there are a huge number, the cost and infrastructure difficulties under that scenario are terrible.
I would still argue that they've got a better track record for fault tolerance than cell phone networks, which are also limited in reach to begin with.
Also regardless of major natural disasters, such as Hurricane Katrina, there are piles of smaller less predictable phenomena, such as tornados, flooding, blizzards, and wild fires for which radio is a more effective medium for reaching people.
There's still no suitable equivalent for the emergency broadcast system for cell phones, and even if there was, I'd be hesitant to stake my life on it in non-urban areas across the US (which is, lets face it, a big part of the country).
And the cell tower business is a whole lot younger than the radio tower business. Time is eroding the uptime edge radio has possessed as cell towers proliferate and get better.
And regarding local disasters. I always thought local events / local news / local weather etc would be the saving grace for most radio stations, the competitive advantage that Pandora could never take away. I no longer believe that to be the case so much. The threat is more Facebook, and other services, than Pandora. As people are all now connected on Facebook, and constantly share local news and events. I believe that may nuke the radio business the same way Craigslist nuked newspapers on classifieds (and not just Facebook, it's one example of a trend in new ways to distribute local events).
Towers are often isolated, a long distance from people (ideally at high'ish elevations of course).
So someone with a grudge, maniacs, whatever, can pretty easily sneak up to most towers and cut a guy wire. It's not difficult to topple most radio towers. And it's not very difficult to get away with it, given the isolated nature of most towers; you're also not going to likely kill anybody doing it (except maybe yourself).
"Safety is a giant concern. AM and FM radio stays available when the power goes down. Cell towers and the Internet do not."
I own radio stations, and that's one of the dumbest things I've ever read about the business. Having suffered through countless extreme winter storms and electrical events, AM and FM radio DO NOT inherently stay available when the power goes down. We have generators at the tower sites and the office, but that can be done at cell towers and elsewhere, there's no magic to AM / FM. Generators do not run forever, and they don't always kick on perfectly. Completely bogus claim on the authors part.
In fact, frankly, more than a few times it was extremely difficult to keep our stations on the air during severe storms (hello physical, outdoors receivers - both at the towers and the office, hello ice and wind and snow), and meanwhile I was able to use my smart phone for Internet access.