Also:
"Few if any legal systems have a process for reliably donating works to the public domain. They may even prohibit any attempt by copyright owners to surrender rights automatically conferred by law, particularly moral rights. An alternative is for copyright holders to issue a licence which irrevocably grants as many rights as possible to the general public, e.g., the CC0 licence from Creative Commons." (Source: http://en.wikipedia.org/wiki/Public_domain#Dedicating_works_...)
I suppose the better question is whether someone can rescind their license for their work and prevent future legal use of that software. I'd like to think that's not possible either, but I have no clue to be honest.
No it can not. Someone can stop releasing their previously BSD licensed code under the BSD license, but all the existing copies people got under the BSD license are still governed by it. This is exactly the same as with the GPL, or any other license.
The copyright holder grants you a license, and that license can be revoked, wether it be GPL, BSD or Apache or whatever, and it applies to _all_ the softwares the copyright holder has rights to - ie all previous versions.
That is the reason why FSF and GNU encourage copy-right-assignment to the Free Software Foundation - as a kind of guard against any one hacker messing with a project.
BTW this copy-right-reassignment to FSF is similar to how Record Label companies reassign the copyright from their slaves, erm sorry, musicians/artists onto themselves and then govern them.
The only reason this doesnt happen more is that most freedom software has many authors and a change in license would require consent from them all. But a really nasty person could still decide to rip his copyrighted pieces out of any previous version thus crippling the whole project.
But nobody is an asshole like that, but legally the possibility exists.
This is not true. None of the standard BSD licenses are revokable.
I could release software under GPL, not accept any patches, see the software grow and 2-3 years from now when a lot of people are using and depending on the software, bam I revoke the GPL from all previous versions and impose a special EULA in its stead. I can because I am copyright holder.
Yes, so GPL fans go by "today me, tomorrow you" and this BSD-fans go by "freeeeedooom" but then dont really put their code in public domain - instead maintain their copyright over it - which grants them the rights to revoke or change their license at any time.
BSD-license can be revoked by the copyright holder you know.
So if all these BSD fans really are "freeedooom", please public domain everything.