I'm sorry, but I think that was a really bad analogy. Besides that, the fact of the matter is, if it can be re-programed with a higher version, it can be reprogrammed with a lower version. They have locked out older firmware twice now, and the only 2 reasons I can think of why is either serious security concerns or firmware o/s licensing issues.
It doesn't matter how drastically different the data (o/s in this case) is, the process of programming the eeprom or flash rom is the same. The chip doesn't care what you store on it. The only thing preventing you from downgrading AFAIK is a version check or something similar in the firmware update routine. I imagine that if you were to physically access the chip and remove it, you could easily burn any version you wanted onto there. Way back when, I had an Asus A7N8X. Asus in their grand wisdom, let slip a bug that would corrupt your bios after making a change then using "save & exit". Once it happen, your MB would no longer post. This happened to me, and the only solution was to reprogram the chip off the board. I paid another programmer to do this for me, since at the time it would have cost more to RMA the board, and taken longer. Then I bought a stacker unit that allowed me to use a physical switch to switch between a primary & backup bios in case it happened again.
Point is, you probably can go back to an older version if you have the right equipment, or are willing to pay someone to do it for you.