It is a tough spot for Iran indeed.... Perhaps they thought that not signing would be considered tantamount to reveling a secret weapons program and so they chose to sign in order to mislead - deception being a good move of political strategy perhaps. After all, is it ever wise to reveal to potential enemies what you are NOT going to do?

I think that expecting anyone to remain without such weapons indefinitely is silly. Every nation is going to want them - some will sign treaties to imply they don't but its only a matter of time. Eventually, they're going to get them. So, as you say, we have to figure out how to live with that.