The difference in spelling is due to the fact the word for Uisce Beatha was brought into the English language twice. Once from Irish Gaelic before the Great Vowel shift in English and a second time from Scots Gaelic after the shift.

Japan also drop the e. Japanese whisky is quite interesting though, some of the stuff is completely out there (eg using seaweed as flavouring) and other stuff could be mistaken for being a scotch. I seem to recall reading that a lot of Japanese distilleries were trained in Scotland.

Last year I had a bottle of whisky from India which I’m pretty sure also dropped the e. That too was a lovely drink and could easily have been mistaken for scotch.

Whisky is not a region of Scotland. The use of Champagne is protected because it's a region of France.

Scotch whisky has to actually be Scotch—i.e. from Scotland. Whisk(e)y can be from anywhere.