I wouldn't bet anything either, but they seem to last longer.

The the stainless bearings for our planes is an alloy called 440 C. Unlike most other stainless, it is magnetic, hardenable and is less corrosion RESISTANT. 300 series stainless has a much higher resistance, but cant be hard enough, at least for our needs. There are also the "PH" types (Precipitation Hardening) stainless's that can be hardened, but it's not as common in our bearings sizes and can't be made as hard as the 440c type.

Finally, I had a stainless bearing get rough and I'll have a look see at it this weekend.