The plastic is most likely Ultra High Molecular Weight, high temperature and MoS impregnated plastic which may last longer than the older style stamped steel cages. I'm sure that engineers take into consideration that the wear of the steel cage material would add hard abrasive material to the grease whereas wear of the plastic would not add hard abrasive and may actually add modifiers that would ultimately help grease performance.

Sounds like the bearings and the races where in good shape. Good luck!