They use the word "organization" instead of "church" as a result of their past objection to religion. Remember, "Religion is a Snare and a Racket". They also avoid the word "church" because they want to "be separate from the world" and since so many christian religions use the word "church" they decided to use the phrase "kingdom hall".
JWs, why God's organisation and not His church?
Well, I come down on the side of clear distinction between the FDS and the other sheep as crucial to survival for them.
I have noticed that in many press releases and statements to official courts etc, they use church in an across the board way to refer to all witnesses. Done to confuse the issue? Or just because they assume all will know what they are talking about when they do so?