Purely my expierence:
1) First stages, so long as they are taken care of, last a very long time before needing rebuilt.
2) Second stages, especially those used quite often, do need more periodic rebuilds, perhaps not annually but definitely more frequently than 1st stages for best performance.
Best guess as to why comes from the enviroments the 'active' parts work in. First stages tend to be sealed and pristine environemnts. 2nd stages get water and other particulates (in the water) feed through them as well as air. Good thing the parts for a 2nd stage are pretty cheap......