All countries lie, it's part and parcel of diplomacy. Expecting otherwise is to naively anthropomorphise states.
And while Israel does have a covert nuclear program that's more or less an open secret these days, it's not directly comparable to Iran. That's because Israel is considered by its neighbours, despite the rhetoric, to be a rational and stable nuclear power that does not have regional ambitions. Israel's nuclear doctrine is explicitly understood by those in the region to be defensive doctrine, intended to ensure Israel's survival rather than to exert influence and control over the entire region.
Iran, on the other hand, does have regional power ambitions and both the intensity of the religious beliefs held by many of those in power combined with its opaque civil and military governing structures mean that its neighbours are not convinced that the country would be a rational nuclear power. Sunni states like Qatar, Saudi Arabia, Jordan and Egypt are incredibly concerned about what Iran could do if protected by a nuclear umbrella and free to use its affiliated groups like Hezbollah to destabilise the traditional Arab powerhouses of the Middle East. That's why the Wikileaks cables have shown Arab leaders to be even more strident than the Israelis in wanting US action against Iran.
So in the end, it's not about who is the biggest liar or who is spreading FUD. It's about the fact that Iran is a country which has potentially dangerous motives, a stated desire to regain 'lost' influence over the Middle East and a covert nuclear weapons program. Any one of these would be cause for concern; the presence of all three combined is the reason so many countries are worried enough to regard military action as a viable option.
