Yeah, but there are extenuating circumstances. I was a Fireman and then an Engineer (fire apparatus) for 7 1/2 years in my earlier life. Worked Forestry fire program and city stuff.
You have to understand the small and medium engines (the actual trucks, not the motors) are usually vacuum assisted brakes and they go from off stone cold to full RPM and full load accelerating out of the barn in like 45 seconds. The older trucks are carb'd and have manual chokes. They may run rich for up to a minute as they come up to temp...
The larger engines are air brakes, but they are hose hooked to the shop air compressor, so they do not have to wait to build air pressure. They also go from stone cold to full RPM in maybe a few seconds longer.
We changed oil at 500 miles, grease, brake adjust, etc. New air cleaner element or wash the oil bath after every fire outing. They can be pumping under substantial load in smoke and embers. Things get filthy quickly ...
Our trucks were mandated to run Delo 400 15W-40 unless they were at Susanville, Truckee, or some other very cold spot. Then they got 10W-30. This was before anyone heard of 5W anything ... No synthetic oils. All premium dinos. Even then the reasons were given for better (thicker) residual film strength on cold start. They sit in a big garage and never freeze, so it all works fine.
If we were on extended fire duty (like I did three fires in a row ending up in SoCal), we had to come off the line to get serviced at 1,500 miles - no questions. And we beat on those trucks mercilessly day in and day out. Stone cold to 70 MPH as fast as you could shift them. Runs from NorCal to LA on the governor the whole way. The only time they idled was between assignments. Maybe an hour here or there. Or, they idled all night long if you were on perimeter watch. Had to, to keep the batteries up and the radios hot ...
A fire trucks life is not as easy as it seems ... Yes, they would go over 100,000 miles if they did not age off the line first. A commercial truck on the same chassis would be expected to go over 300,000 w/o major engine work. We might roll a set of rods and mains in at 50,000 miles. Usually when they were getting clutches ...