What difference does it make that the reason for the cancellations was announced? The fact that the cancellations were announced based on any reason at all would be sufficient for the terrorists to no show. The better practice would be to let everyone board the flight, taxi out to the tarmac, and then unload everyone on to busses, wouldn't it?
On the other hand, I am glad that we are not letting the apparent lack of cooperation go unchallenged.
I too considered this very question. My concern would be that this tactic could end up as a hostage/murder situation.
I concluded that a better tactic would have been to announce a slight delay of the flight(s) then carefully filter out the suspects before they ever boarded (including the crews).