Just thinking about the line of argument used in that talk...
If it's a good thing to "keep on the watch" by thinking Armageddon may happen by a certain date, then is it possible for anyone to be guilty of false prophecying for that? If so, how?
The undercurrent I get from that talk is that because JWs declare Jehovah's name and the truth on other issues (that's another subject to be sure!), then they can't be false prophets.