Black Attorney Quota in SV?

Recently, I had a discussion with an African-American (A-A)attorney in the Valley and he was telling me how firms in Silicon Valley had an unwritten quota limiting the number of A-A attorneys in each office. His understanding is that hiring partners feel that A-A associates either don't fit the "culture" or are limited to employment groups where they can be used as a black face to defend clients against claims of employment (racial, sexual, age, etc.) discrimination. I could not imagine that such an assertion could be true since I figured the Valley was fairly progressive and would be intersted in hiring as many qualified applicants as possible. In fact, he told me to check the NALP directory and look for myself. The results were truly amazing:
(All are SV offices unless otherwise noted)

Allen Matkins -- 37 Total Atty -- 1 Part. , 0 Ass.
Bingham McCutchen -- 60 Total -- 0 Part. 0 Ass.
Clifford Chance -- 49 Total SF/SV -- 0 Part, 0 Ass.
Cooley -- 224 Total -- 0 Part, 1 Ass.
Cooper -- 55 Total (SF) -- 0 Part, 0 Ass.
Davis Polk -- 29 Total -- 0 Part, 0 Ass.
Dewey Balantine -- 23 Total-- 0 Part, 0 Ass.
Fenwick -- 256 Total -- 1 Part., 3 Ass. (Down from 7 in 02')
Gray Cary -- 146 Total -- 1 Part., 1 Ass
Heller -- 80 Total -- 1 Part. 2 Ass.
Gunderson -- 60 Total -- 0 Part., 1 Ass.
MoFo -- 108 Total -- 1 Part., 0 Ass.
OMM -- 98 Total SV/SF -- 0 Part, 1 Ass.
Orrick -- 78 Total -- 0 Part, 0 Ass.
Pillsbury -- 82 Total -- 0 Part, 0 Ass.
Skadden -- 47 Total -- 0 Part, 3 Ass (up from 0 in 02')
Thelen Reid -- 28 Total -- 0 Part, 0 Ass.

There are many other firms in SV listed on NALP. To be fair I chose offices larger than 25 attorneys and those that were better known (presumably creating a larger recruiting pool). If anyone can explain these numbers please let me know. No office had more than 1 A-A partner and the vast majority of offices had either 0 or 1 A-A associates. This definitely appears to be more than an accident.