The Stats are different for the Staff of Destroyer and its actually worded quite differently on it.
When firing the Staff of the Destroyer, nominate a direction. Then Roll 2d6 and extend a straight line from Imotekh's Base in the chosen direction, a distance equal to the total rolled. Any Unit, friendly or enemy, under this line takes a number of hits equal to the number of models in the unit under the line.
Thats the exact wording for Staff of the Destroyer and that is worded so you only take the amount of hits to the amount of models the line touches. Death ray is worded about the same way with such a different confusion mechanic on the 12" then a line deal that a quick read makes it sound so much better than it actually is.
Edit: I understand why they Used Within on the Death Ray its so you don't overextend and touch your own troops but i still stand by this argument.