The answer to the first question is that somehow people appear to be expecting Israel to strike. Why Israel? Quite simply put, because from all the countries potentially affected by Iran's Nuclear weapons, Israel is the one most at risk. Also because of precedent: when nobody was willing to act decisively against Saddam's Hussein Nuclear reactor in Osiraq in 1981, it was Israel that bombed it. When Syria started to raise her ugly nuclear head, it was Israel that bombed their Nuclear facilities.
The answer to the second question is far more complicated. Iran had, at this point, spread its nuclear facilities all over its territory and it is building backup facilities for each one of them. If and when they completely duplicate their network, they would enter into what Sarkozy called "the immunity zone". In addition, the wide dispersal of the existing facilities and the distance from Israel makes any airstrike from Israeli bases a one-way mission.
Until a year ago, Israel could count on logistic support from Turkey and the use of Turkish airspace, but as we know things have changed and that option is now closed. The other problem is that a one-way strike reduces greatly the possibility of success. For Israel to succesfully destroy the Iranian facilities, a necessary condition would be to operate from bases closer to the target. This can only be achieved with support from Arab countries for land bases or the United States for the use of aircraft carriers on the Indian Ocean.
But even assuming Israel is succesful in destroying the Iranian facilities, can it destroy them completely? so completely that the possibility of retaliation will not exist?. The situation is similar to the one that existed between the USSR and the US during the Cold War: MAD (mutual assured destruction).
The difficulty with this scenario is ideological. Israel would consider the strike successful only if it survives, since that would be the main reason for striking at Iran. Iran, on the other hand, is currently lead by a group of ideologically motivated dictators, and Ahmedinejad appears to be convinced that he has special role to play by ensuring the destruction of the world to precipitate the coming of the Mahdi (Muslim version of the Messiah).
So we have, on one side, a country highly motivated to strike but which will hesitate to do so unless it has a reasonable probability of survival. On the other hand, a regime with a religiously based ideology convinced, with good reasons, that one way or another it can survive the first strike better than Israel. Iran also announced publicly that it will retaliate in case of an Israeli attack. But Israel cannot attack without a minimum of logistic support closer to Iran.
According to experts, Iran is 18 months to two years at the most away of building a Nuclear device, and is developing missiles that can reach not only Tel-Aviv, but Rome and Paris as well. Israel recently announced the succesful test of an automated aerial vehicle (a drone) with the capacity of carrying a payload over a long flight.
In short, the world is coming dangerously close to a confrontation with Iran and the pieces are falling one by one into place. In the meantime, Israel has an existential question to answer: To strike or not to strike - that is the question.