Looks like it was stored under the grinder and got an unhealthy dose of grinding wheel particles (or sandpaper particles, grit of some sort) to grind the <bleep> out of it like that. My 25 year old 690 has no similar wear pattern, and it does get used.
Yep, several of my Porter Cable routers have wear like that (although not that bad!). It's from steel or abrasive particles getting down in there. You can feel it grinding as you twist the body, but you just keep going....and it gets all scored up like that. I've repaired mine by filing them gently to remove the raised ridges, cleaning thoroughly, and waxing them.
