I'm old enough to remember when buying Minecraft Alpha included a promise that the code would be made open source some day. IIRC it was "when I'm tired of working on it", which given the success it's been is probably never. (For some value of "I" that's not Notch.)
I would probably go back on a lot of things I've said if someone offered me over a billion dollars. Also minecraft being as popular as it is you would end up with a lot (more) pissed off clueless users. cf kodi.
