That's kind of odd considering that the failure mode of shock absorbers that are overheated is to pop their seals and lose pressure. I'm sure with a pile of them to set on fire you could figure out a way to make them go boom. Sounds like a "it happened once therefore policy change kind of thing", but I'm not qualified to judge firefighting techniques.
The thing about bumpers just sounds plain dated. Nothing's had bumper shocks since the 1980s and most sedans don't have an appreciable amount of metal in the bumper to the point where it's about as structural as the core support and the time would be better spent on a different part of the problem. Citation?
x2 about cabins being designed for survivability though.
There are definitely elements of the fire service that are - for better or worse - "this is the way it's always been done".
In some ways it works. It doesn't noticeably change your efforts or effectiveness, just your tactics, and now you don't need to question "is this a feature of this car?". Just like "what cars use extensive magnesium in the engine block?" or "does this vehicle have airbags? did they deploy? how about side airbags?" Just assume they do, and use a commonality of technique.
There's definitely a challenge between reconciling techniques that work in the field and textbook operations, and then keeping both up to date with the latest 'discoveries' - for instance forty years ago many fires were contained by a lack of fuel, nowadays it's a lack of oxygen (better sealing, even with ventilation systems) and higher fuel loads (petrochemicals in homes and furniture) mean that oftentimes by the time we get on scene you can have this home that is a darkened down box, thick black smoke with little or no visible flame, hotter than anything, and as soon as you open a door, you have about 90 seconds to get some cooling applied, or you're going to have flash over by virtue of all the oxygen you just supplied to this nascent fire.
The thing about bumpers just sounds plain dated. Nothing's had bumper shocks since the 1980s and most sedans don't have an appreciable amount of metal in the bumper to the point where it's about as structural as the core support and the time would be better spent on a different part of the problem. Citation?
x2 about cabins being designed for survivability though.