Sarcs, Not all GPWS systems are created equal. Each manufacturer can use slightly different algorithms to interpret terrain differently. It even comes down to what terrain database they are using and and how the algorithm interprets rate of closure.
I believe at LHR quite a few GPWS were used to test the approach and only some of them sounded a warning. I am pretty sure the CASA test aircraft GPWS didn't sound a warning, but I do know that the RAAF one did.
This scenario has also causing some issues at Gladstone. This was solved with the GPWS system in question needing a terrain database update.
In short, a precedure is not pulled if it satisifies the criteria of the day and is test flown as suitable. Just because some systems sound a warning doesn't mean the procedure needs to be withdrawn/redesigned. It more than likely means the system is too outdated or not refined enough to deal with these types of terrain issues. The problem is at the system end, not the procedure end.