I was just reading TomTaz's thread on how he thinks Nightwolf may be involved, and although I don't like the idea, it is entirely possible in a way.

So it got me thinking of exactly how Raiden would be killed.

I think it would an idea that maybe the DK captures the Earth Warriors, and he says to Raiden that he can take their place so Raiden does what he does and gives in for his beloved earthwarriors and agrees to swap himself for the release of them. Only he is deceived and once under the power of the DK he is killed, and the earth warriors remain captured.

This could explain the Deception, and also why the earth warriors are not really involved with this game.