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Some bicycle bearings are likely more highly stressed than automotive wheel bearings, considering how short-lived they are even if well lubricated.
Now, I haven't had the chance to put tens of thousands of miles on any set of bearings; end up upgrading or whatever sooner. But my experience has shown the bearing failures are typically due to poorly adjusted preload (either too tight or too loose). ... Seems somewhere like 100% of the wheels I've found coming from various suppliers had grossly over tightened bearing preload. Even many brand new hubs, though I have found that the nicer units tend to be more appropriately set up from the factory.
I've "put tens of thousands of miles" on several sets of bearings. (Over 300K lifetime cycling miles) Generally they don't last nearly as far as conventional car wheel bearings, even if meticulously adjusted and not intruded by water or dirt (a common cause of failure). I agree about the all-too-common tendency to adjust bearings too tight, which is easier and quicker than adjusting them correctly. Those modern "nicer units" often have sealed cartridge bearings, which don't require tedious manual adjustment.