On CPC, bus arbitration is done on every CPU bus access. On MSX, bus arbitration only applies to M1 machine cycles but access to VRAM has other limitations. On ZX Spectrum, bus arbitration is done not by using the /WAIT pin but by disabling the CPU clock when needed.
The NOPs column corresponds to CPC timings, which account for the bus arbitration managed by the [[Gate Array]]. The NOP instruction takes 4 cycles. This is the minimum amount of cycles an instruction can take.
Instructions LD (IX+d),r and LD (IX+d),n surprisingly take 5 and 6 NOPs respectively, even though they are both listed as 19 (4,4,3,5,3) cycles in the datasheet. This happens because LD (IX+d),r has one less memory access operation to do compared to LD (IX+d),n as it does not have to fetch the operand from memory.