[butlerm]

A dash is definitely not the same as a minus. A hyphen however is so close as to cause a serious ambiguity, so much so that they call the standard character a hyphen minus. So if someone comes along and invents a minus or a hyphen that is distinct from a hyphen minus, and can't even be visually distinguished most of the time, that is not particularly helpful for general use.

People want to use Unicode for everything, when some things are really typesetting abstractions that should be avoided in general purpose computing. Groff and troff have their peculiar exceptions for historical reasons, but surely in retrospect it would have been better for a hyphen minus to render as a hyphen minus rather than as a hyphen.

As far as Japanese goes, the keyboard mapping there is unfortunate. Perhaps they should have considered using a shift key or something to shift between hyphen minus and dash. And in my view those ought to be two characters with typesetting variations, not six or seven.