that doesn't quite compute for the following reasoning:
as you say, some BSD code is used in microsoft windows. microsoft windows is licenced under the microsoft windows licence, even though it still contains the BSD code. it can do this because it complies with the requirement to nod the cap towards those regents of the university of california.
I think that if a GNU OS tipped its cap in the same totally legal way, it could simply release an OS that used BSD code but under the GPL instead. i don't see the legal difference from the point of view of the BSD copyright holders.
however it is shocking to me if the BSD licence really did actually prohibit GPL code being released (by being rapeable, it would discourage others from writing code to do the same job, in fact the only reason alternative GPL TCP/IP software (for instance) was written for linux was that BSD was the subject of a suspicious court case at the time. all other OSs of note, as i have heard anyway, use some BSD code in their TCP/IP software (if they have TCP/IP in the OS anyway)


