I wonder if this is BE vs. AE. I wouldn't use a comma in your examples from #4.
Breaking the "Why" apart from the "no" is foreign to me. Here's how I'd say it.
// Is that XYZ? - Why no, it's ABC!
// Did you XYZ? - Why no, I ABCed!
CM2DD, I also wouldn't put a comma between "Why" and "Bob", in your example, far be it for me to come between them.^^
Even when I say it to myself, there wouldn't be a natural (comma) pause. It'd run together: Why Bob! You look sad today. Why aren't you happy/smiling?
The "Why Bob!" part, even though using an exclamation point, is a sort of question for me, borderline interjection. It's a hybrid of sorts.
It's just me. Sorry
if I'm way off base.
I've been trying how to imagine translating some of the examples into German using "aber nein", and they don't really add up.