This link may interest you...
I don't know anything about it but think for fixed grips they remove chairs and replace a few parts like pins, bushings, nuts etc., then re-install the chairs in a different spot. Look up at the cable some time, you may see several colors of paint marking where the chair was. Then they slap a new coat of paint on the cable and r&r'd attachment which makes it EZ to tell if its slipping.
As far as the towers and bullwheels and power system components...??? My guess is there is quite a bit of maintenance. Perhaps its easier to maintain detachables.