While it has certainly turned out that way, considering the process of dissemination, both Snowden and Manning dumped a pile of documents on a third party. It's that third party that, in the case of Manning's files (WikiLeaks), was hasty and cavalier in its release of information, whereas Greenwald/Poitras/Etc. have been more careful and deliberate in their releases.

To the extent that the individual leakers could have some sort of culpability, it would be for the people with whom they chose to share their information, though I grant that the who is not independent of the how.