In fact the Kerberos technology is based on open source and it seems that MS had promised to release its modifications quite a while ago. When users realised the modifications were copyright protected they decided to publish way to go around them and so had to publish some (all ?) of the modification specs.
Plus there is the 'trade secret' issue: as soon as something is published on the web it seems it can't be considered a trade secret anymore (well that's what I got from the articles I read yesterday, but I am no lawyer...).
Plus the fact that MS does not seem to attack directly the persons who sent the controversial posts but rather Slashdot that only has them on it's discussion forums. One part of the Slashdot answer is that MS is not liable for messages posted through hotmail or other services that it owns etc etc.
JC Helary