LJR - no, the rest of the world does not use QNH.
In UK Civil Aviation uses QFE for instrument approaches if I remember correctly.
As far as trying QNH, at great expense Lady Belinda Buck's lover introduced QNH in the RAF and we had to try it.
Once his flies failed we then reverted to QFE.
One the inches/mb question, on the Vulcan the rule was quite simple. If an American controller, being helpful, gave a setting in Millibars we had to ask for it in inches and then two of the crew would convert it to millibars.
Now we use hectopascals I guess it may all be different.
