Stringy:
Ok here I am with egg on my face....
I was going from memory on how the mast receiver goes together without actually looking at it, and making too many creative assumptions about manufacturing without actually going back out to the garage and double checking things that I worked on 3-4 yrs ago without a further thought since then (haven't had any problems in that area since then).
First off you are correct there is no brass insert in the bottom of this mast receiver as I described. Here is a pic of one of my old mast recievers.

I distinctly remember rebuilding a piece that had a brass bushing, and the area around the bushing was all crushed and split about 4 yrs ago on one of my TI's, apparently it was not the bottom of the mast receiver that broke on me (I've ripped out several of those studs, and have had to repair that area in the boat a few times in the past). Obviously I don't remember what the exact problem was or what I did to repair it correctly.
You are also correct that the mast receiver does not have to be removed from the boat in order to replace the plate, working from my flawed memory, I was thinking the plate was screwed in from the bottom (not the top), so mistakenly stated the mast receiver has to be removed anyway, which is incorrect also.
It's funny how you memory can play tricks on you (unfortunately your memory is the second thing to go as you get older (LOL)). But I do distinctly remember repairing a severely elongated hole (the one the 1/4" stud goes thru) that had a brass bushing in it, where the area around the bushing was crushed and in pieces on one of my older hulls, looking back at it now, it must have been the brass insert in the hull itself (not the mast receiver). Too many TI's and repairs ago I guess.
Knowing my steels very well I am still willing to bet that on the thousands of Islands out there you can count the number of failed pins on one hand, and if you were to trace the actual failure cause, it would be flaws in the material itself rather than from some fatigue factor, where if it were a material fatigue factor eventually they will all snap off (I doubt highly this to be the case).
How Hobie handles stocks replacement parts is entirely up to them, being from manufacturing myself I know how expensive it is to maintain huge inventories of repair parts, and it is likely the sub assembly is supplied complete to hobie from a sub contractor. It is also likely Hobie does not own the tooling for these sub components and has little control over them ( they are likely buying a complete assembly from the sub-contractor, as one catalog number). That's pretty much how the world works these days.
I'm guessing that if a dealer reports a warranty repair because of a broken pin, they will receive from Hobie a complete mast receiver, where once they get it, they would remove the plate from the new unit, screw it into the old existing unit, then throw the rest of the parts away, that's pretty much how almost all manufacturing works today. On your car if you blow up a 3 cent resister on the computer motherboard, you get charged two grand for another computer which just plugs into the car, and the old one is thrown away, pretty much the same with TV's (I used to be a TV repairman LOL).
Stringy, you are entirely correct.
Bob