If it's mechanical, it wears away eventually. And the auto manufacturers like everyone else are looking to save a $ when possible. So it would not surprise me if some of the parts GM uses over the years have different reliability factors.
I never took too much of a look at it, but I think almost all my GM cars had a "maintanance schedule" in them. If I recal, it gave timelines when to change certain things beyond just fluids (such as when to change the bearings or shocks or struts). It would be interesting to see what GM says to what you're seeing with your car.
What you are explaining is why a lot of people don't want a car hitting 100K, lots of stuff starts to need attention. Going back to my current daily car, the '94 Grand Am, I have owned it since '03 at 86K on it. I've done shocks/struts, a wheel bearing, control arm bushings, ball joints, later a whole control arm and half shaft, outer tie rods, radiator, exhaust (I had the exhaust done at a shop), intake gaskets around 90K, head/intake gaskets at 180K, O2 sensor, heater core, 2 coil packs and I think that's the big tour of stuff (in no particular order). All in 86K-200K. Some people I know feel that's unexceptable, and the car breaks down all the time. I scoff at that. As it sits today, I would not hesitate taking that car on a long distant car ride. Factor, I had a CHEAP and short lived car payment, did the work myself. It was a trade off.
Heck, I was impressed the factory heater core lasted so long it blew almost the moment the car passed 200K (plastic inlet/outlet tubes cracked, that was a funny day to me), that was impressive compared to other n-bodies I knew!
Win some, loose some. But again, you can have some cars that really exceed your expectations and others that really don't. Most of mine have met my expectations. Like I said, for a while, I began to despise the 3100 (I knew a lot of people with it, so when one had a problem, the others followed. But like I said, I look back on it and actually that Grand Am has served me well and still is. A have a friend with one that I'm amazed the car starts (his needs all new suspension and oil changes have been really neglected).
He's actually buying my mom's '97 Grand Prix once I get a chance to do the intake gaskets and a wheel hub on it.