UK Altimeter Setting Regions vs US single altimeter setting
Something that has been puzzling me for a while, and one that I can't seem to get a definitive answer on.
Within the UK the airspace below the transition altitude is constructed of 21(?) altimeter setting regions, whereas the US uses just a single standard setting of 29.92" Hg across the entire country.
What's the reason behind this, other than the obvious of not having to change the altimeter subscale on a regular basis? Conversely, the profile of the land in USA varies massively, surely it would be better to use several ASRs?
Any help would be much appreciated!