I may well be wrong but I thought all modern altimeters were corrected to a standard ISA lapse rate of 2 degrees a thousand feet and a standard ISA day of sea level and +15 C. Any temperatures below 15C result in the altimeter (which has been corrected to +15 at sea level) under reading. For very low temperatures this under read can be quite marked and consequently a correction has to be added to avoid flying into the granit.
To a certain extent you are all right. The altimeters are corrected to give a true height on an ISA day, buit also have to be corrected due to the unsafe under read on cold days.
[This message has been edited by Don Coyote (edited 28 November 1999).]