Playing devil's advocate here, since the EAS network typically has an AM station as its Primary Entry Point, couldn't the FCC dictate that automobiles not (a) create interference with the reception of EAS stations, and (b) all automobiles must be able to receive EAS Primary Entry Point stations.
I could see a day in the future where an event happens, and an EAS message goes out telling listeners to tune to the Primary Entry Point station for updates (especially since most EAS Primary Entry Point stations are "news" stations).
Granted they could say that the Primary Entry Point station is also simulcast on FM or a Digital sideband, but as others have mentioned, FM signals don't propagate as far as AM, and not every car has a Digital sideband receiver. I remember as a kid we were driving back to my hometown in East-Central Kansas from Tulsa, Oklahoma (July 1981), and about the time we reached Coffeyville Kansas, we could pick up the AM station in Kansas City (about 150 Miles Line of Sight from the Transmitter), and they were broadcasting continuous updates on the collapse of the skywalks at the Hyatt Regency Hotel. We ended up listening to that station for a couple of hours as the reports continued to come in. Obviously, this example wouldn't prompt an EAS activation, but you get the drift - you couldn't do that level of coverage with an FM station.
