Oly's receivers use to have to be "fit" together at the factory cause they didn't have the machinery they have now. Their new CNC lathes mills produce upper and lower receivers that fit togather right out of the machine.
IMHO, "tight tolerances" was meant to indicate quality, but it was really to backtrack on rifles that made it past quality control with improper fitting. For those rifles that were improperly fit, "tight tolerances" applied to everything in the rifle, from the selector lever not turning freely to the takedown pins needing a punch to push out.
Thats all different now, and you can tell the difference between new and old production. Old production has a painted on looking finish, and the new stuff is anodized.
Overall I am happy with my Oly rifles and customer service has been outstanding in my many experiences with them. You cant go wrong buying Oly.
Edited to change "lathe" into "mill".