For what it's worth:
I average 1500 miles per week. Yes, per 5 day period (I don't drive the truck on the weekends-it's my office). Since my original
brake pads are still at 75% , it is obvious that this truck does not see "normal" use-it is, literally, 98% highway mileage.
Since I keep records of every mile driven and every gallon of gas purchased, I can tell you exactly where I was, the weather condition, the passenger and cargo load in the vehicle, and the gas mileage for literally every
mile driven. I doubt any of the "experts" out there have records anywhere nearly as complete as mine.
When I pulled the plugs at 50km there was no obvious reason to replace them. They were as clean as could be expected for something 7 months old-the difference being that mine had two, three, or more years
of use on them at 50,000 miles. There has been no
performance or mileage degradation from 10,000 miles to 100,000; the only reason I changed them now is because even though they ran fine, the 100k is as good a benchmark as you will find. If I drove "normal" use, I would be much more concerned and probably would have changed them long ago. The fact is this: they didn't need it before this, they didn't really
need it now, I just did it.
And if I may, I would caution you against telling me your
high standards of expectations
are any higher than mine, because in my profession, I literally place my life in the ability of my vehicle to perform. rms8 is correct-while someone else's may not last 100k, mine obviously did.