Fireflybob and all.
There is noting wrong with healthy debate and in fact it should be encouraged.
The London TMA is somewhat unique in its design. As a TMA North controller, the correct QNH setting is critical to a safe operation as the majority of my SIDS have an element of a step climb to them. Both my Heathrow SIDS (BPK and BUZAD/WOBUN) climb straight to 6000 feet. However underneath I've got Luton departures climbing to 4000 of 5000, likewise Stansted's doing the same not to mention London City and Northolt.
It may seem a bit of a pain in the bum having to repeat the QNH, but trust me I have lost count of the number of times someone has called climbing to FL60 or have "bust" their level because the wrong QNH has been set. It may have not resulted in an incident, but it has on other occassions!
What is more "fail safe"? An actual QNH readback with the associated cross checks from the pilot, or an assumption that the correct QNH has been copied (often by one pilot only) from the ATIS?