Roger,
I think I am understanding your point. Let me elaborate by example...
Bicycle hubs, which is more durable and easier to repair...
Set of Phil Wood hubs with sealed cartraidge bearings...
Or a set of Campagnolo Super Record hubs with cups, cone and loose bearings...
Both hubs are extremely well built, beautifully designed, and very expensive. The Phil Wood hubs are CAD/CAM machine-made with some hand-assembly, while the Campagnolo hubs were very much hand-built after the initial forging and machining.
The answer is not as simple as you think...
Phil Wood hubs are virtually indestructible, easily 80,000klms before needing any type of service and you can service a set of hubs in 10 minutes or less with a change of bearings, but the bearings are essentially unserviceable since they are sealed mass-produced, albeit very low tolerance, cartridge bearings. So while a set of Phil Wood hubs will last several generations, are the easiest to service, they depend on a disposable part for longevity.
Back to the Campagnolo hubs with loose bearings. With skilled and regular maintenance, these will almost last forever. But servicing the hubs requires an about an hour of a skilled mechanic who knows how to adjust the cups and cones since improper adjustment will result in ruining the bearings, which will require replacement of the bearing races which require even more knowledge and skill along with specialised tools.
So which one is more durable, I have seen Phil Wood hubs ridden by cycle messengers at the rate of 25,000klms per year for years in any kind of weather and conditions, without any service whatsoever. I have seen a set of Campagnolo hubs ruined in 6 months because the rider is sloppy with service and did not repack the bearings after a riding in a few days of rain.
There is a huge amount of engineering and design effort going to make things last longer with less maintenance. The product as a whole will not last as long as an older product, but will last longer than the older product with less service. The consumer wants to do less and less maintenance and would prefer to not think about something until it breaks, then simply replace with a new.
I do not necessarily agree with this philosophy, but then not everyone knows how or wants to know how to repack their wheel bearings, maintain their car, etc and etc.
So one hundred years from now, Phil Wood hubs may be irreparable if the required cartridge bearings are not available, while the Campagnolo hubs will stay able to be repaired and serviced if the knowledge, skill and tools exist. So yes, I concede products that are designed and largely made by hand may enjoy a longer longevity in the end...