Before their release, British PM Tony Blair had said that the next 48 hours of negotiation would be "critical." This hints that he had privately threatened Iran with military action if they didn't release the hostages. However, the AP gives Blair no credit for the release. Instead, they credit Iran's top foreign policy negotiator Ali Larijani who "[w]hile a religious conservative, Larijani is seen as a pragmatist with close ties to Iran's supreme leader, Ayatollah Ali Khamenei."
The AP sees this development as a warning that the West should go easy on Iran in the future so as not to enrage the "hardliners":
As Iran headed back into talks with Europe on its nuclear program Thursday, it already was warning of retaliation if the West pushed too hard.
This analysis would be more plausible if it wasn't the one that liberals always use. In a typical example, the 1933 New York Times fretted that Germany had "extreme" Nazis and that Hitler was trying to moderate.
UPDATE: Former Sen. Fred Thompson comments on the favorable treatment that Iran's Islamists have received after the hostage release:
Some in the West seem part of Iran's propaganda war; claiming that the release of the hostages was a victory that proves the Iranian dictatorship can be reasoned with. To misrepresent unpunished piracy as a victory is as Orwellian as the congressional mandate banning use of the term "the global war on terror." What are we — Reuters?