Take the history of OpenOffice. Pre-2.0 didn't require you to install Java. The problem is that Java VM is a commercial product controlled by Sun. By restricting Java VM to certain platforms Sun can potentially kill OSes they don't like, because with no OpenOffice (now also MySQL) an OS can be considered dead. This is worrisome - well, for those who don't trust Sun at least.

Except that, you know, Java is going fully open-source. VM and the whole works.

As I wrote below, yes, somehow missed the news about JVM, but the thing is, as an example, MySQL is GPL'd too and it is not quite open (and I still don't get it how they managed to take GPL down that way).

As far as I know, they keep a dual license; every change in the code goes for both licenses, excepting those changes they want to keep closed, those going only for the non-GPL license. Only the real owner of the software (not the licensee) has the right to do this kind of stuff with GPL.

Please correct me if I'm wrong in my guess.

You got it right. http://forge.mysql.com/wiki/Code_Contributing_FAQ has more information.

Other companies with a split proprietary/free model require copyright assignments for contributions as well. So, too, does the FSF, although for rather different reasons.

Just checked their web site - you are right.

There is a language spec, you can write your own VM (I wouldn't recommend it...).

Actually JVM is GPL'd already, somehow missed the news, so it's not that worrisome.