The JW concept of preaching the "good news" is quite a paradox.
What they do is combine two differant messages and ideas togeather in oder to maintain a false view of what exaclty they are doing.
1. Good News of Gods Kingdom - This is their message that the earth is to be turned into paradise soon. This is what they will link with the "good news" of Matthew 24:14
but wait, they have another work they are doing as well!
2. The "Warning Work" - JWs teach that they are simultaneously preaching the good news while participating in a "warning work" about how the present system is soon to be destroyed.
JWs are taught that these two things are mutually exclusive, but in reality they are not. If you ever point out to a JW other religous groups that have converted just as many people to their theology in around the same amount of time (mormons, seventh day adventists, ect.) they will still give you the line about them not doing the "door to door". But this is not a case where these other groups have failed in teaching and converting (e.g. preaching the "good news") but rather that they have failed by not participating in the "warning work". Thus they now can claim that they are the only ones doing it. (not to mention that because they only have the right interpretation of the message only their "good news" could be the right one)
Like many other exclusive groups they have found ways to define what they do in such a presice manner that nobody else on earth could ever be shown as doing the same. Practially speaking they are actually giving two messages, but they would never admit it.