Simple, my avatar sharing friend.
By submitting their mix to OCRemix, they are subjecting the mix to be controlled by DJP, allowing him to do with it as he choses, while of course not claiming ownership of the mix.
Why submit a mix if you don't acknowledge the fact that that is how it has been since day one?
Do the two comments you quoted contradict each other? Pretty much, but it was a basic unwritten law here before it was blurbed before.
DJP should allow someone to remove their mix if they wish to, like DoD does, but you choosing to submit a mix here should show that you are aware of all risks that goes with your decision.