Assange tried (at least he claims he tried) to get the US government to help him remove names that it felt should not be released. The US government refused. Which is perfectly understandable: why should the US government tell Wikileaks exactly which names in some leaked documents are the names of actual US government informants? That would be stupid.
Assange then chose to release all the material anyway, putting the life of anyone whose names were in that material potentially at risk. Newspapers, in the same position, did not publish the names. Whether you agree or not with either action, the fact remains that they are clearly different actions, and that one involves publishing people's names and potentially putting their lives at risk and the other does not.