No actually.
Subpoenas are an investigative mechanism. Nobody goes to jail (directly) because of a subpoena. It is used to establish the “these are the facts” of a case. It is the traditional legal mechanism to shine light on something.
From what I’ve read, the US Justice department thinks it is very unlikely that they can mount an effective court case against Assange and Wikileaks over the publication of the leaks. There is too much precedence in the other direction (specifically the Pentagon Papers) to pass muster in an American court. The legal precedent in the US is that if someone gives you classified information and you publish it, that you are not criminally liable; regardless of what the foaming at the mouth commentators would wish to be true. Anyway, neither the UK or Sweden would extradite for such a case. Facing two, high legal hurdles, they’ll want a very strong and airtight case before pushing ahead. What they are likely investigating is whether Manley was in contact with Assange while he was still doing his downloads and if Assange encouraged him; and more importantly, whether it is provable in court. That is an entirely different affair if Assange encouraged the downloads, because it becomes espionage.
Birgitta Jonsdottir is likely the weak link if that is indeed the case. She is possibly the one who put Manley in contact with Assange. We know that she lacks discretion, having taken Assange as a guest to a function at the American Embassy in Iceland, so it is not surprising that investigators may feel that they can gain relevant information to the case there.
I find it funny and ironic that self styled openness activists would be up in arms about a subpoena. I take that back. I find it sad and disheartening. I agree with what Assange says in public (e.g. his statements during his TED interview and his op ed in the Sydney Morning Herald), but Wikileaks’ secretiveness reminds me a bit too much of the pig in Orwell’s Animal Farm.