Pulling back from the specific (tampering with routers) to the general ("spying"
doesn't make it less so.
The implication was that people should not buy Chinese made equipment because of the terrible Chinese spying. Meanwhile, people should not buy American equipment because of the equally terrible American spying.
You can't simply reduce all of the NSA's activities to "spying" and conclude everything is okay because the NSA is supposed to be "spying." NSA doesn't have a mandate to conduct unlimited "spying." It's supposed to be conducting intelligence on foreign communications. Not Americans' "metadata," not Google's network, not routers that may end up anywhere.
Speaking of which, when Greenwald was on Colbert last night, he mentioned coming across an internal, unofficial statement of NSA's current intent. The gist was that NSA sought to collect "everything." Something about, "grab it all, sift it, store it, process it."
"Everything" collection is not the NSA's mandate. And that is the problem that's been uncovered here. Communications intelligence agencies all would like to have "everything." They have always sought to do this, and the law and U.S. civil rights have always limited it. In the new War on Terror world, NSA has again found ways to exceed its mandate and pursue intrusive communications gathering well beyond the scope of its authorization. It's not surprising, but that doesn't make it somehow okay.
As for "vague," you're reading a news report discussing an excerpt of a book. To conclude Greenwald's work isn't sufficiently detailed without actually reading it is baseless.