The Obama decision would be more understandable if it were part of a secret deal to get Russia’s help with Iran. This Guardian story suggests that’s not the case:
Russia hinted that Obama’s decision would not be met by any swift or generous concessions. The country’s foreign ministry spokesman, Andrei Nesterenko, described the move as “obviously a positive sign for us” but made clear the decision had been a unilateral one taken by Washington alone. He suggested there had been no deals with Moscow on Iran or other issues. “That would disagree with our policy of resolution of any problems in relations with any countries, no matter how difficult or sensitive they may be.”