Dude. They have the content of email too. I'm going to make a wild guess here and assume it falls under the "required by law" category of the denials. Well, too bad for them, too bad for us. Welcome to the future, and there's scant chance that any of this will ever get rolled back.
Meanwhile, its also fairly obvious that some security folks sympathetic to the NSA have your ear. You like them, you respect their skills, and social heuristics dictate that you give their opinions due weight. They haven't been overly impressed with the recent leaks and reportage, and why not--we always bristle when the media covers something near and dear, and bristle again when it is sympathetic to the wrong parties.
Back to the contents of email again. How, precisely, it is done is of course very interesting but also an implementation detail. The fact is this kind of content would have been considered very valuable, and therefore effort would have been expended to a) explore the options and b) make it happen.
If you go back over the past few years of leaks, a recurring theme is, it has happened, and it appears to have been achieved via legal compulsion plus some fairly vanilla engineering. However, we may also assume that any serious collection effort would necessarily include redundancy of methods, so if for some reason legal compulsion were to end, the collection could still continue. And this is were we find ourselves today: legal collection at nominal risk, but the program itself secure.
And we know we are here, not from any one specific claim (possibly garbled, possibly wrong), but from the pointillist painting rendered by years of such claims, where the negative space provides as much structure as the positive. So yeah, you don't like Greenwald et al on aesthetic grounds. But Greenwald is also irrelevant to the overall narrative here, which is "when we became cognizant of our pervasive surveillance." Why would they not have the contents of email?