Why does someone has to have created the Xel'Naga?

Have in mind that the Xel'naga only evolved the Zerg and Protoss, they didnt create them.

And I dont think that Duran is the overmind, as you said he should've had killed Kerrigan if that was the case.

Hopefully Blizzard wont just make this a "Oh blast the Zergs come again" game, they will probably add several twists and turns to make the story even more intruiging.

"The Xel'Naga have never been said to have gone into hibination"

Perhaps Duran just said that they were sleeping becouse they have been absent for a very long time.