The issue here (as I see it
) is that Iran, as a signatory to the NPT are re-starting a program that could be used to attain nuclear weapons, whilst no longer negotiating on a method of verifying that the uranium thy produce will be used for non-weapons use only.
Other nations that have/may have nuclear weapons and are not signatories to the treaty are no less an issue, but are not bound by the same rules. (although as already stated, India, Pakistan and North Korea openly admit their nuclear capabilty, and Israel is still making no denial or admission) None of these states are currently saying they will not develop them (although NK is still saying it will in return for light water reactors) or that they will increase their arsenal...
There was the same amount of concern when NK dropped from the NPT, and also when Pakistan tested a nuclear warhead.
Leaving the usual US bashing aside - Iran signed the treaty, and agreed to be bound by it - now they are refusing to have their compliance checked - that is an issue for the UN..
The statement to "wipe Israel off the face of the earth" is nothing new - many Muslims are opposed to the existance of the state of Israel - Rhetoric and bravado are nothing new in the middle east.
The Iraq situation has made people nervous.
Those countries that fear they may be next (Iran and Syria have been bandied around in the world press), and the rest of the world who wonder if that fear will be translated into paranoia and stockpiling, which may well lead to a new "cold war", only this time the sides would be based on religion rather then government.