Thanks for your response. It's interesting that you apparently also are familiar with luthiers. I originally thought of this question because some musical instruments appear to have effectively infinite (or at least longer than several centuries) useful lives.
My luthier has some knofe blades made by a now-dead artisan and he says they're better than anything now being made. Nobody knows exactly what was the secret. For watches, it may not be a matter of a secret: I have read that modern movement parts are normally hardened only on the surface while older movements (at least the better ones) may have been hardened all the way through. Through-hardening doesn't mean that they won't wear, it just means that after then thin outside surface has worn away they will still be hard. I have also read that machine-based production methods may require softer metals than older production methods. I don't know if either of these things is true.
I don't think there is anything nefarious about producing parts that may wear quickly. Especially in the case of a movement maker that is willing to supply spare parts, the best value for the consumer may be in using an inexpensive fabrication process and assuming that there will be occasional replacements. I don't feel as happy about it in the case of makers that do not supply spare parts, as they are effectively maintaining a monopoly on the servicing of their watches, and that can be inconvenient and expensive. The biggest concern, though, is what happens once the supply of spare parts is exhausted. I'm starting to think that I should greatly reduce the extent to which I wear watches for which I cannot easily get replacement parts.
That raises the question of time frame. I have many watches in the 40-50 year old range that seem to have been worn a lot, don't seem to have had replacement parts, and still keep excellent time. If the wearing-out period is, say 100 years for a top-quality watch in full-time use, perhaps I shouldn't worry too much, as I will not likely outlive the watch. (In this context, for top-quality old watches, I would define wearing out as losing the ability to keep time reliably to within perhaps five (preferably few) seconds per day.) So now my question has changed: what watches can last the longest in good condition without replacement parts?