I'm pretty sure the New York Times was given info from Manning and refused to follow up. So...
And they sat on the warrant-less wiretapping story for a year.
Nevertheless, I think that supporting Greenwald and Miranda's paychecks is a worthwhile cause. They're taking a far greater hit here than the Guardian is, but the Guardian is supporting them. So an effective way of supporting Greenwald and Miranda is to support the Guardian.
If papers such as the independent, etc. had been given this information, I'm sure there professionalism would have been the same or higher. Outside of handed-on-a-platter reporting, the Guardian has massively cocked up in the past (leading to the arrest of sources, etc.).