@jayeless Well, given that the English language has many words and expressions that have completely changed meaning over time — sometimes to the opposite of the original — I try to just shrug it off (though there's always a little niggle that slips through). Like you, I think it makes no logical sense at all.
@Miraz You're right, and like I said I'm easygoing about most of those minor changes. (Like double negatives – if you really want to say not the negative, you emphasise it, so "we don't need no education" is not ambiguous, really.) I think this one just bothers me because it confuses me in a way most of these minor quirks don't. "I could care less" is illogical as well, but at least it's always pretty obvious what the person meant… with "all X is not Y" I always have to go back and do a double-take because I assume the literal meaning and then figure out that can't be what they intended, haha.