I think you misread my post Bookworm
You're right, I did. I should have pointed out how wrong you were, not complimented you on the excellent point.
I was actually trying to point out that the obstacle clearance on a precision approach can be so small that the altimeter error does become significant. Just because there are occasions when it isn't doesn't invalidate the principle.
The chosen DH on a precision approach is
not your guarantee of obstacle clearance -- your adherence to the glideslope
is. If you remain on the glideslope a late decision does not compromise obstacle clearance. By contrast, on an NPA, your MDH
is directly connected to your obstacle clearance.
It is utterly daft to ignore a known and predictable altimeter error of the order of 50 ft for a NPA where obstacle clearance might be as little as 246 ft.