You lightweights! My outfit (or at least some of it) is approaching 160,000 miles
Aha! no wonder it's fucked! 
GC
On the other hand I know how reliable machines get past 60K... and I guess you do to now

it's perfectly possible to keep them going indefinetely, but after a while you end up spending the cost of a replacement (either in cash or time or both) just to keep it going, and then you need two bikes just in case something major goes on your "main" bike, and then they each get half the maintenance so the breakdowns get more frequent.... and so on and so forth until you end up with a double garage full of spare bikes just to keep one on the road

(ringing any bells yet?

) fine if it's a hobby, but when it's your primary means of transport it becomes a pita!
If I want to continue enjoying the lifestyle I do my bike has to behave like a car, it needs to start and be useable 99.9% of the time, if I can't trust it it affects my livelihood and indeed relationships adversely in many ways (eg fail to make appointments once or twice and you become the guy who is unreliable, even if you made it on time fifty or sixty times before...).
There is a very big difference between hobby bikes and workhorses, both have their place but they have very different requirements. A workhorse can often do both, a hobby bike....