For someone who doesn't want the story to be about him, he sure talks a lot about himself...
He's trying to gain public support and put pressure on the US government, while at the same time persuading countries to give him asylum. Releasing a statement will help him to do this.
Works either way.
You'll notice he never once mentioned the documents or their contents in this message. He's not "making the story about himself" - he's using the media as a tool to apply pressure to the forces aligned against him in the hopes of securing his safety.
As someone else said, remaining silent lets his opposition control the discourse. You can see this clearly in the frenzy of stories in the media about Snowden's stripper girlfriend and the "IS HE A COMMIE SPY?" headlines. Providing a counterbalance makes it harder for the government propaganda machine to sway public opinion against him and turn him into Just Another Terrorist.
A 'counterbalance' can often instead be a distraction which is what I fear happened here.
I, for one, was grateful for the update. Yes, I care about how Snowden is personally doing in Moscow.
If he chose silence, he'd be infinitely detained, and would receive no justice.
That's his fundamental problem, after all. If any of the countries he intends to flee to were to have someone leak the same kind of documents that Snowden leaked about the US, that person would be prosecuted to the fullest extent of the laws of that country.
So when you talk about justice, I don't think you want Snowden to receive justice, because that's a small cell for the rest of his life, or worse.
Joan of Arc stood for France, in the Hundred Year's War. The story was not about her, it was about the country, the people. But yet, her narrative, the ideas she had, her martyrdom, etc all had a profound impact on the events of history, and lead the changing of the tides of the war.
A war is not fought on a martyr's backs. Sometimes, it takes 22 more years for the job to be finished. This doesn't mean putting someone up as an example isn't warranted, nor is it dilute or make the narrative of the people any less powerful.
If he goes entirely silent then the government will step in to fill the void: "His girlfriend's a stripper, he's a hacker terrorist, his neighbors say he's weird, he might be a soviet spy, he did it all for the attention, he's not an American."
If he speaks out on a daily basis the news media will eventually grow tired of the story and move on leaving him to be a 3rd page story when he's arrested.
His best option right now is to stay in front of the news for as long as possible until some solution is worked out. In the meantime staying positive with the American people will do more good for his eventual trial.
A common theme among people who oppose Edward Snowden's is to criticize his character. Even within this thread people have resorted to name calling, dubbing him a "Drama Queen" and accuse him of seeking fame.
I suppose it's easier to attack a person than it is to attack the issues he stands for.
All his globe-trotting and statements just detract from the issues he's raised re: surveillance.