There's a huge difference between EU demanding a country to comply and EU going to war.. Iraq was threathend several times, when they refused inspectors to do their work, I realize this kind of situation is different, but I don't believe anyone is really interested in a war here. No one is that stupid, Iran would be thwarthed and we could leave immediately after, we wouldn't hold any moral responsibility to restore them like in Iraq.
And both EU and The US are tired of war so it would take something much more radical than a hostage situation to provoke us to war.
Jorian, you seem to forget the power of words and political means to an end. It's far more beneficial in these matters (in the long run) to use a harsh political tone than physical reprecussions. Especially since EU and US are trying to restore their reputation in these days (especially to their citizens), which Iran is, cleverly I might add, taking advantage of. We would loose more if we go to war and they gain international reputation by staving us off. They are trying to see how far they can push us.