Whether or not Mojang "owned" bukkit has little to do with whether anybody is in a position to make the project's license valid. Also, he was OK with the state it was in for years, before he finally decides that he's going to block the entire project in order to "force" their hand? That makes little sense. The idea that Mojang would open source their code is also fairly ridiculous. I still think the whole GPL thing is just a convenient excuse.