DIY: Rear Differential Oil Change

Fountainhead

I'm gonna make an observation here based on what I've seen. I've never changed my Diff fluid, at 13K I'm probably not due unless I'm bored one day. My opinion is that when guys remove the magnetic plug and see the metal shavings, isn't the magnet doing it's job and keeping those particles out of the bearings and so forth? I would put forth that the diff fluid, while it may be needing to be changed due to heat/age/wear and detergents decaying over time, the metal filings on the drain plug aren't a sign of the fluid needing to be changed, but merely a sign of the diff magnet doing it's job.
Maybe I'm misinterpreting what I've read but that's the impression I get.