The thing is that NSA was engaging in a shadowy campaign. It wasn't possible to conclusively prove or disprove it. This story isn't. It's making factual claims, that there are physical backdoors in hardware that is publicly available. From then on its possible to settle the matter by buying such a motherboard, and using this to produce hard evidence of the backdoor. It wasn't possible to go to the nearest NSA field office to get yourself a copy of XKeyScore.