Firstly totally agree that QNH passed by ATC is a mandatory readback.
If I call to get a clearance prior to start/pushback and advise I have "Info X" why do I need to state the QNH since this is normally passed again when I call for taxi and the readback is mandatory?
If I am inbound (on a Flight Level) I will be passed QNH when cleared to descend to an altitude and this also requires a mandatory readback so why do I need on initial call to pass QNH?