David Weaver
...in my use, but I've seen abused planes just as Joel has (and you have) that may give someone the notion that a completely worn out plane is normal.

I'd imagine that anything worn out either planed dirty wood (or wood with foreign objects in it) and was intentionally abused, or was used for a single task and due to the low cost, abused when it was trued (as in belt sanded or run across a power jointer).

I've got one try plane that has probably trued about 750 board feet of cherry, beech, walnut, rosewood and mahogany. I've trued the sole once (how much, I don't know - the thickness of a sheet of paper or two) as the only thing that I can find that actually puts fast wear on a wooden plane is dedicating one to jointing a whole bunch of rough lumber with no other use (they'll wear hollow in the center).

More common to find a used plane with a spent iron or a replacement.

The treatment and constant tuning of japanese planes makes the relationship go the other way (n bodies per iron and n irons per body in western are probably not that different of an n)