FlexibleResponse, you are of course quite correct about erroneous G/S; my post focussed on false / multiple beams.
I agree with the points that you make, they are always worth restating, either for those who did not know, who have forgotten, or just as a good reminder of an essential safety item.
I also agree about the NZ accident; there is a very good CD / video on the incident (from NZ CAA and/or FSF?); the FSF report can be downloaded
here.
There was a similar event in Brazil involving a 777; a preceding aircraft checked the OM altitude and questioned the QNH – then adjusted the flight path; the 777 with all of its sophistication did not check the OM altitude, but was ‘saved’ from a terrain encounter by EGPWS. Although a technical fix for the particular problem is not available (ILS ground test mode), the industry has (or should have) put defences in place to prevent a repeat of this type of incident, but OM altitude checks are still required as these defences are only as good as the person implementing them.