That's not 100% true though, but for the most part it is. The moment Israel demonstrates that they do have the bomb; for instance by using one or exploding one for test purposes the perception of Israel would change and this in turn would cause a change in attitude towards Israel. It would also telegraph what kind of yields they have which would say a lot about their capabilities. They are clearly very much aware of this and that is the main reason for the 'refuse to confirm or deny'. Some things are more powerful when left to the imagination of the perceived enemies.