I am a developer, a game developer even, and while I can very well see how a task that seems easy like this one can reveal itself to be reaaally complicated and dangerous to fix, I don't see why they made that much of a deal of this.
"It took me several tries to find the correct way to fix this", is, well, pretty much common when dealing with bug fixes. And it's hardly medal worthy or anything, this is just their job. When I do happen to fix a vicious bug I'm quite happy with myself, but I don't get interviewed by our community managers like I did something so incredible it needed that many lines in a weekly update.
Also, I still don't understand how they managed to get this bug ONLY on the heavy weapons. Must mean their code is full of weird exceptions and special cases, if all of their weapon types are not handled the same way on such a basic feature as "respawn with the same amount of ammos you had". Finally, I don't know why they need to compute this value *again*, instead of simply storing it before dying and retrieving it again when respawning...
tldr: as a seasoned game developer, this bug and this weekly update puzzled the hell out of me.
The vault thing, though, is a case of a really complicated task disguised as a "wtf Bungie you could do it in 10 minutes tops!".
People fail to realize how much things need to be changed for this to be implemented, in a UI that was not designed to allow for scrolling areas.