<p>I think he probably means that a low-ish Writing score isn't going to carry the same mark of disapproval as a low-ish CR score, but it could still cause adcoms to get all frowny. (Cripes, I know I need more sleep when I use phrases like 'get all frowny'.) A 600 in Writing is not going to be equivalent to a 750 (unless the college explicitly states it won't consider Writing scores!), and the kid with the 750 will be preferred, but it might not be the same degree of differentiation (especially if the Math+CR are comparable) as in the case of greatly different Math or CR scores.</p>
<p>At least, that's my interpretation. I don't know to what extent that's actually true -- I suspect very little, because Writing does actually test useful skills, and is probably worth weighting into the equation.</p>