The staement the person is making is relative to the pixel size.
If you take a picture with the D800 and then say a D700 (or other FX camera) with the same amount of hand shaking (or subject movement) and then print both photos the same size, the amount of blur will be identical. However, if you go pixel peeping, since the D800 has more (and thus smaller) pixels, the same amount of motion blur will effect more pixels. Another way to think about it is if you go pixel peeping on a D800 you are looking at a much larger overall image than when pixel peeping on say a D700. Thus the blur looks worse. But again when compared between the same size images, it is the same.