Last time I looked CASA exams still had those Cessna performance graphs where you went around the boxes rather than the real tables found in section 5 of the POH...
I've had this discussion at length with a CPL ATO who insisted on candidates adding the 15% factor on to figures in a Piper POH with CASA approval page or he would fail them...he wouldn't budge.
I also blame the old AFMs for a lot of the old wives tales floating about and some of the "one size fits all" procedures that don't take the POH requirements into account, particularly cocnerning use of carb heat and electric fuel pumps....