A foreign policy staffer on the Hill has a different spin on the disclosure of that Obama letter to Medvedev than the one I offered, namely that the U.S. leaked its contents:

Had assumed our side leaked the letter, in part to pressure the Russians to come up with a serious response after not responding or providing a vague initial response.  The U.S. proposal comes across as very reasonable, so maybe this was psychological ops to pressure the Russians into saying yes.
 
And the placement in a Russian newspaper can be explained by our Embassy in Moscow leaking the letter and hence making its origins less obvious.
 
I don’t get how the Russians would gain from leaking a letter putting pressure on them to do the right thing, especially when it neutralizes the feared U.S. missile defense shield. 

The argument I heard from experts yesterday was that the letter's initial appearance in the Russian press suggested a leak on that side, with the Russians hoping to lock in Obama's talk of halting the U.S. missile shield in Eastern Europe. Murky stuff, clearly.

--Michael Crowley