You don't hear about it because DET doesn't seem to stack well. It takes a pretty large amount of it to make a noticeable difference. I think you will find some where on here that someone did the math and 1 stat point is worth something like ~6DET. Also, I am pretty sure that the healers DET affects how much they heal for and that the DET of the target has nothing to do with it (I could be wrong about this.)