Like Valdarious said, there is an option to toggle it in the config menu, and its set to "on" by default.
Its just very very rare. But it does happen, and sometimes its pretty funny. I had the option for slow mo deaths turned to excessive and with limb loss on and was fighting a reborn. On the first hit I land, I chop the poor chap's lightsaber hand off. So the time slows down as the camera begins to pan, the hand holding the lightsaber flies off to the side, while the reborn is in his death throes grasping at his missing limb. It was one of the most hilarious moments in a game i've ever experienced. It was just so perfect hehe. Reborn says "the force will betray you", and I do this to him
Anyway, its there, its just pretty random and somewhat on the rare side.