It's a pissing contest.
What does Iran have to gain from bombing Israel, let alone the United States? A mutually-assured destruction? Ahmadinejad is too weird for the Ayatollah and inner tensions have increased. I remind you this is a theocracy after all. Ahmadinejad is merely the puppet of Islamic extremism, and he STILL freaks them out. The horror, the horror.
As for Israel there might be some cause for concern. Seeking to show their strength, there is the possibility of a "preemptive" strike, justifying the reason for President Obama's clarity in statement. Make no mistake about it, this is a volatile situation. But when has that not been the case? The middle east is a black-hole of volatility.