My understanding from listening to watch people is that old lubricants tended to degrade over years which meant that watches back then needed to be serviced every 5-10 years regardless of use. Modern chemistry means they're much more stable, so a watch can last indefinitely on the shelf, but will still have tiny amounts of wear while running (thus hard-on-hard bearing surfaces - jewels - are used to extend the life). I find it a bit ironic that these advances were made after mechanical watches have become close to deprecated for actual timekeeping duty.
the effects of errosion can be mitigated by using a lower beat too - this is why some of the big names in independant watchmaking have been pushing for lower frequency watches - to extend the service interval, I believe George Daniels wrote about it before his death.
