Note that the wording (where they say that "many" of the tips "led to dead ends") implies strongly that "many" others DID BEAR FRUIT. Otherwise they would have simply stated that "all" or "virtually all" the tips were useless. Instead, they merely pointed out that "many" (they didn't even go so far as to say "most") did not lead to useful information, making it clear that a large portion of them *were* useful leads.
But that's not the impression the authors seem to be trying to give...
i noted in my response that, similar to your observation, the CNET author of this piece appears to have a poltiical axe to grind. Which is really a shame; you'd think that an information site like CNET would be able to remain apolitical, even on this issue, and just present the nuts-and-bolts of what the NSA has been doing. But the part that you pointed out, as well as a half-dozen other spots, led me to feel like the author was trying to lead the reader by the nose to form an opinion on the subject, rather than simply passing along information to aid in a reader's understanding of what the NSA did.