Very strange, isn't it?
"So" used thusly has kind of bumped "well" out of the way as the nervous-first-breath stalling-tactic syllable.
Like "ah" and "um", only "so" carries with it that Lizzy Warren aggressivenes, as in "so I am going to tell you how it works because you are far too stupid to figure it out yourself."
That is a perfect explanation.