[howard941]

> And only A can be directly written to or from memory

I think the author might to write that only A can be indirectly written to or from memory but even that isn't correct as demonstrated by the code bits that retrieve and store from and to ram @HL (and IY/IX+blah). The 8080 was able to directly read and write HL. The Z80 could do it for IX, IY, and IIRC BC and DE too.