I always check the shaft-to-bushing clearances on a standard rebuild, but more often than not they are within .0005" of the original specs. The replacement bushings that are currently offered (by only one supplier nationally) have greater clearances than most slightly worn original bushings. In the TR6 distributor, as Keoke stated, it can be a major machining process to replace the bushing, or I can install a 2-piece bushing as the factory did in some models (to clear the tach drive gear.) In Paul's case, the shaft bushing had almost .001" tighter clearances than the replacement bushings. I could have custom made a bushing that fit .0005" tighter, but you have to ask why? It wasn't cost effective or necessary, even with points!
At this point I am shopping around to have better fitting bushings made in bulk. I think I found a great supplier, but have to be worked into their schedule for a small parts run (less than 10,000.)
By the way, most rebuilds can be done for $79 including new springs, so automatically replacing a good shaft bushing wouldn't be fair to customers. I'd have to raise EVERYONE'S costs, whether it was necessary or not. This way each part is evaluated on a case-by-case basis.
Jeff