The upshot is twofold: First,
there is no good reason to suppose that differentials in brain size
are not attributable to dietary and other non-genetic variables

Actually there are two good reasons. First of all because the same differences are found at birth. Meaning it would have to be prenatal.

http://dx.doi.org/10.1016/S0160-2896(97)90004-0

Second because the difference isn't just cranial capacity, but the entire structure of supporting post-cranial skeletal traits. Such an integrated set of traits is not plausibly the result of developmental insult.

http://dx.doi.org/10.1016/S0160-2896(02)00137-X

whatever correlation between brain size and IQ exists must be
weak enough to allow for women to have the same average IQ as men despite
having smaller brains

Women and men have different brains in a lot more ways than different populations do. You are ignoring Saletan's statement that blacks and whites matched for head size don't differ in IQ. That is not true for men and women.

http://dx.doi.org/10.1016/0160-2896(94)90032-9

Saletan explains this finding away by noting that military
recruits are already pre-screened for intelligence. The trouble is that
the very same brain-size data Saletan uses to bolster his hereditary
interpretation of the IQ gap is originally based on measurements of
soldiers

False, that is one paper on *head* size, not *brain* size. Read the review paper Saletan links: the data for racial brain size differences comes from multiple methods, including MRI and direct brain measurement at autopsy. The different methods are in agreement.

http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&Te...

http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&Te...