What are those washers for? I recently serviced my FH-RM66 and was surprised to find that the cones have a couple of washers in the middle. The cones are monolithic, so the weashers can't be holding it together or absorbing vibrations. 

What purpose are those washers serving? And how were they mounted in there?
That washer is a part of the "seal" system for the hub.  If you look at the hub there is a lightweight metal cap pressed into the hub over the area of the bearing race, and that washer (which is plastic) fairly snugly fit into the hole in that cap.

This doesn't create a water-tight seal, but it's tight enough to keep out a lot of the dust.

I've never studied closely how the washer is placed there.  I would assume that the cone is made of two pieces that are swaged together during manufacturing, but I can't say for sure.