It's a fair point, but I'm kind of getting tired of responding to it. I think that such an absolutist stance can be more harmful than helpful in some situations, and that view is backed by my anecdotal but not-insignificant experience.
Some officers do not care about your rights or the law, and if you demand a lawyer when they ask how much cash is in the vehicle after they pull you over for doing 37 in a 35 zone, then you and your lawyer are going to spend a little while dealing with the matter.
Whereas if you give nothing away while remaining polite and courteous and aware that you are probably being lied to, you might drive off with a warning. You might still need to fall back to "am I being detained", but you might not. Sometimes you simply can't completely avoid a conversation, especially when the other party can physically compel you and make up an excuse later.
There is no universal good advice for such difficult and varied situations, and acting as though there is doesn't do anyone any favors. That's why I like this article and commented on it; the author provides useful knowledge and references without being overly prescriptive.
And incidentally, the absolutist "never speak at all" part of the James Duane talk comes with the caveat, "if you are being suspected of a serious crime". The article seems to be more about officer-knocks-on-your-door or traffic stop sort of situations.