I was reading an article recently -- I think it was linked here -- about how the **AA get what they want. Make ridiculous requests, then when they get shot down they offer as a compromise to let us keep doing something that is already legal in exchange for which we agree to give up just some of what they originally asked for.
Specifically, they agree to allow fair-use copying in exchange for us paying a tax on blank media. Anyone who refuses their compromise position is painted as the ones not willing to meet them halfway. And by accepting the deal, we reinforce the notion that fair-use was not really a right to begin with -- which it was -- but is instead something they have granted. (Which can therefor be taken back later.)
Iran is doing the same. Stake out an unacceptable position -- claiming it is their right to develop nukes -- then offer as a compromise to only enrich the uranium. Just a little, really. By accepting the deal, we'd be implicitly accepting the proposition that their developing nukes is a negotiable item.