We men are a little slow when it comes to figuring out what wasn't said, if it was a woman who didn't say it. We men can usually figure each other out rather easily. What we need to do is tune into our mate and learn her signals. I know enough about women to know that when she says nothing is the matter, that she really means something is the matter but I haven't shown enough interest to make her tell me or we're somewhere inappropriate for that conversation at the moment.
However, saying that the success of a relationship hinges on a man's keen perception of his wife is going a bit far. It is equally hinging for the wife to be more straightforward with the man in order to have a successful relationship. Actually, both are true and should both be happening to have a successful relationship! :)
must try to figure out what have not been spoken.
Yep, there should be a balance there. Its important to listen above all, but noticing what isn't said is also a good tool because you can pick up on things that your partner may be avoiding. This can clue you in to things that may need to be brought up that perhaps they are withholding, or that may be red flags.