It's wrong to say that they are reducing freedom.
And it's wrong to say that I said that they (Mandrake) are reducing freedom. They don't as one of their release is GPLed. And they won't as long as both free and proprietary releases will be technically the same.
But they open a way for proprietary vendors to make proprietary versions. Those vendors would reduce freedom, not Mandrake.
And it's not a matter of `are Mandrake good or evil people' or `did they prove their loyalty to the free software movement'. It's a matter of `do they try to achieve their goal (selling service) the right way'.
There are lots of `good people' who have just been wrong at least once in their life....
If you make a change you are not obliged to dual license it.
MandrakeSoft will simply not be entitled to use your modification in their non-GPL license.
And they probably won't use it in the GPL version, so that the two releases keep being technically the same. But that is not a problem as you can release by yourself your GPL-only modifications.
It may be unlikely to happen, but it could be a dangerous game for Mandrake. They could lose contributions from free software developers that are not willing to dual license their work, and they could lose contributions from proprietary vendors... because it is proprietary.
A superior version of their software could be developped but they could not benefit from it, because it would break their strategy (the two versions being technically the same), or because they would not have the right to do so (proprietary copyright infringement). If this superior version is free, it's fine for the community. But if it is proprietary, it's a pity.
Guillaume Ponce http://www.guillaumeponce.org/