If this is so, can you explain why the bearing hole in the gear center doesn't also wear out? There are many many, many things that use a plastic gear, wheel or other rotating or even sliding motion on a smooth metal surface without much wear and last for years. Thhe real probable reason it came with plastic C clips is one of price/money. And there is also a reason that replacements are fewer for the plastic clips over the steel ones, again money. The steel ones have less of a chance of having a burr that will really mess with the gear/wheel, and many people wouldn't trust one made of plastic.