[Zardoz84]

Apple I and ][ Had a machine code monitor on ROM, and on some version had a mini-assembler. Search for Woz's monitor (and take a looks to the assembly code, it's very interesting)

But I agree that Theodores's post there is something wrong. Only Sinclair's ZX81/82 abuse of the Z80 to generate the screen. Zx Spectrum's had an ULA chip that handles the screen generation and other stuff, like the cassette interface.