So am I correct in my understanding that this sort of hack is made possible only...

dools on Dec 9, 2012 | parent | context | favorite | on: Pokemon Yellow hack recodes the game from within

So am I correct in my understanding that this sort of hack is made possible only because the Gameboy uses an 8080 derived chip with Von Neumann architecture? ie. if it used a Z8 (or any other Harvard Arch chip) it wouldn't be possible to "bootstrap" like this?