Andy,
The fabric insulated wiring came long before the breakers. Usually, breakers replaces the old style fuse blocks, so that is why you see the old fabric insulated wires attached to newer circuit breakers.
Most of that old wiring is in pretty good shape, except anywhere it has been exposed to heat, like above a light fixture or in an attic. In that case, the old rubber and cloth covering is completely disintegrated. I have some pictures of this that I will post in a few days.
Peter
