If it's not part of the OS, then how can the iMac access it?! Clearly I'm missing something -- maybe even my mind.
Surely NOT your mind!
It can be accessed because it's a bootable volume that resides on the iMac's drive.
My Terminal excerpt shows that I've got 4 separate volumes - HD2, HDx, HDz, and Recovery HD - all of which are completely independent of my OS (on volume HD), and the same way I can boot into volume HDx (a bootable clone of HD...the others are either data or empty), I can boot into volume Recovery HD.
