Qaddafi didn't come into power through social revolution, like the one that convulsed Iran from bottom up. Instead, he won state power through a bloodless coup d'état. It's easier for Washington to deal with a dictator who rules the passive population, whether to depose him (as in Iraq) or work with him (as in Libya), than with the collectivist leadership who lead the historically revolutionary and still very much politically active population like Iran's.
Let's say Washington offers a deal, and Khamenei, et al. take it. Washington can't rule out that the people of Iran won't, sooner or later, undo it, either restoring the status quo ante or even taking their revolution to a new, higher stage. ========================================== The Iranians, of course, are not the only people to have made a revolution. The Soviet and Chinese revolutions of the past century - which were both more thoroughgoing than Iran's in that capitalism was eliminated - demonstrate revolutions are more easily reversible than we could have imagined.
It's theoretically possible that the people of Iran can become the exception and prevent any similar accomodation by their leaders under the pressure of the capitalist world economy. They might even one day take "their revolution to a new, higher stage". So might the the Chinese, Russian, and other peoples of the world, for that matter. But that's hardly the basis for analysis and concluding that the foreign policy of Iran was substantially different from that of Libya in the two decades leading up to the Iraq war - the provision of fighter places by the Soviets to the Libyans notwithstanding.
The USSR and PRC commonly sold arms to countries like Libya, India, and Pakistan, who were not part the "Soviet bloc" - except, that is, in the minds of US Cold War propagandists. No more than the Islamic Republic of Iran became part of the "Western bloc" when the US supplied it with arms through Israel for use against Iraq.