The difference is that you are working as we were taught. The OP is doing something on a completetly different level. I have never seen ANYONE crawl under a trailer unless an emergency(on road). If I have a faulty valve(leaking), I take it to the shop and let the mechanic crawl under and get dirty.
One thought about inspections. I still don't understand how a vehicle can come out of PMI and no grease is ever disturbed. I have had the same tractor for several years and it has had undisturbed grease and road grime on critical steering components, suspension and so forth. It's never been cleaned or wiped down for years. How could you possibly look for cracks etc. without being able to see the metal and components? I suspect it's never looked at. Or skipped on the list. I suspect this is why a drag-link could just fall off.
I don't know how they trained you there, but here, we are trained to get underneath the trailer to check that the 5TH wheel lock has been engaged around the trailer pin. There is no way to see that unless you shine a light directly behind the 5TH wheel, underneath the trailer. When I check the rear of the trailer, I use a rubber mallet, and I get underneath the trailer, check the tread of the tires, make sure that I can see a cap on the stem of the inside tire, I shine my flashlight on the springs, get directly underneath the trailer and check that the air tank's welds are solid, then thump both brake chambers with the mallet, check the inside side of both springs, then get back out from underneath the trailer and resume the pre-trip outside of the trailer. From there, I thump the tires, check to make sure the outside tire has a valve stem cap, the hub has oil, the lugs nuts are solid and rust-free, make sure the marker light is lit and do the pre-trip on the rear of the trailer. Then, when I'm on the other side, I lean under the trailer and check for a valve stem cap on the stem of the inside tire, check the springs and thump both tires, check outside valve stem for a cap, hub for hub oil, and lug nuts, secure and rust free.
The reason I go all of the way underneath the trailer in the rear is for three things, to thump the brake chambers, to make sure the welds on the air tank is solid and to make sure the metal washer on top of the springs is secure underneath the U-bolts. All of these things I check are from experience. The brake chambers? I once pre-tripped a trailer, the chambers were fine, but when I reached my destination, one chamber was barely hanging on the frame. If that would've fallen off while I was driving, the brakes would've locked up. Ever since, I get under there and lightly thump the chambers to make sure they are on solidly. The welds on the air tank? We had a driver get written up because he dropped off a trailer that was then pre-tripped by another driver who noticed that the weld on the tank was broken and barely hanging on, on that side. The trailer had to be off-loaded to another trailer. After that, I visually check the welds on those tanks, no exceptions. And as far as the washer above the springs, an older driver pointed this out to me, especially on the railboxes, which have that bigger u shaped washer underneath the two u bolts. He showed me one night his railbox where one of those washers was partially off the springs, He said if he wouldn't have spotted it any big bump could have dropped the U bolts on top of the axle.
Not all of these things are required, but you damn good and well if something happens while on the road, you and only you will be charged with an accident. So, pardon me, but I will always check this stuff, and I won't apologize for it either.