slim-slag
Have no idea why the note is not on the GPS chart.
Also, ALL approaches (except Cat II, III ILS) must use the baro altimeter for minima determination, and definately NOT GPS indicated altitude (unless baro corrected, some higher end sets, and even then, not official).
latetonite
Not unusual. GPS indicates absolute altitude above mean sea level and unless baro corrected, will not agree with the pressure altimeter.
Is GPS foolproof? Of course not, and the same can be said for VOR (beam bending), NDB (night or coastal effect), LORAN (precip static, lane skip), etc. Just another aid to put in the pilots pocket when needed. I can recall when pressure-pattern navigation was used, and at the time figured it was the cats pajamas.
But THEN we had a Navigator...a whole 'nother subject.