I thought I was pretty much exempt, or lucky - but I had a Bachmann Doodlebug literally drop it's wheels off from white gear disease, and now this, and really neither one was hardly ever run. I keep watching my Kato NW2's and I've had a bunch of those and have never had one split, but you know what they say.
The problem occurs not because of heavy use, but the passage of time. The constant stress of the metal shaft inside the plastic tube causes it to crack. You can have cracked gears in a loco that was never ran (but sat on the shelf for 15 years).
I fairly recently posted a fix for Bachmann split axles. I have a similar fix for Kato universals (like the ones used in the RDCs and other locos). Yes even Kato is not immune from this problem.
