Hi Julien,
Sorry I guess the connection is more intuitive than I thought.
Many dictionaries contain as definitions of "Witness" reference to it being "evidence", e.g. Webster's New World: "1. attesting of a fact, statement, etc.; evidence;....5. something providing or serving as evidence." (Barron's Law Dictionary also supports this definition.)
In defining "example", Webster's says thus:
"1. something selected to show the nature or character of the rest; single part or unit used as a sample; typical instance; 2. a case, punishment, etc. that serves as a warning or caution; 3. a person or thing to be imitated; model; pattern; precedent..."
Reviewing Isaiah Chapter 43:
Verse 8, "Bring forth a people blind through eyes themselves exist, and the ones deaf though they have ears. 9 Let the nations all be collected together at one place, and let national groups be gathered together. Who is there among them that can tell this? Or can they cause us to hear even the first things? Let them furnish their witnesses that they may be declared righteous, or let them hear and say, "It is the truth!" 10 "You are my witnesses, " is the utterance of Jehovah, "even my servant whom I have chosen, in order that you may know and have faith in me, and that you may understand that I am the same One. Before me there was no God formed, and after me there continue to be none. 11 I--I am Jehovah and besides me there is no saviour."
So God, via Isaiah is laying down a challenge saying to the Nations, let them furnish their witnesses or their samples and be declared righteous. The nations cannot. Thus he says to the Jews: "You are my witnesses!"
We see therefore that as I mentioned in my post being a "Witness" is in part testifying to God's truths (Just as JWs believe they are doing) but also there is the connotation of serving as an "example" or evidence that out of mankind, a sample can be found that wll be righteous to God. In short, an example can be evidence, i.e. a "witness." In this sense then being one of "Jehovah's Witnesses" is being an example (or sample) which is evidence in the grand courtroom drama of universal soveignty (See Book of Job).
Unfortunately, I am not at home but perhaps someone can dig up the original hebrew here and I believe it might be more enlightening of our understanding.
--Eduardo