Conditions play a very large part in determining component life, as I've found - Wheels for example:

I'm from the UK, and when I used to commute on a road bike (perhaps 20 miles/day) I'd tear stuff to shreds, particularly wheel bearings. A new bike with poorly sealed hubs showed trouble after only 3 months riding, thanks to contamination & corrosion from weather & road salt. Another set of wheels, built using better sealed Shimano MTB hubs lasted better, and would have gone longer but for the mis adjustment they all seem to have from the factory. Same goes for some Ultegras...*
Eventually I had wheels built on Hope Technology hubs because they used sealed cartridge bearings. Very little maintainance needed, and if they do go bad, the whole bearing can be replaced for "like new" performance.

3 Years ago I moved to California and had a rather basic road bike for commuting. It had Shimano hubs with seals, and I've opened them up yearly for a clean/relube - they show no appreciable wear and are still smooth, with pretty clean grease remaining. Up till last year I was covering more miles too - 30 miles/day was typical.

It's much easier to keep bikes in good shape here than back home!

Ed

*Noted elsewhere (but I cant remember where - May even have been Sheldon Brown) shimano hubs seem to be adjusted without taking the effects of the quick release clamp into account. This results in excessive preload on the bearings.