Russia Duns Iran?

Somebody please make sense of this one for me, and don't tell me that Russia just wants its money. My take is that they are contributing dutifully to the 'international community's' desires of smacking Iran around but without coming off like Chimpy's poodle and their treasured self-image of Russian manliness preserved. They do as they are told but save face, win-win. Why else would they stop selling nukes to Iran? I mean aside from oil and some commodity metals, the entire Russian economy consists of selling bad things to bad people. Oh wait, it just hit me. They want to blackmail the Iranians! You've done half the work already, so your customer is locked in to you as a supplier, so can shake them down for more loot. That would definitely be more in keeping with Russia's style. Never mind.