That's the fluff. IF
GW were to rule that the special ability worked with sweep attacks, that would be a good way to picture it. You can't make a ruling based on fluff, though, as fluff can easily be used to rationalize any ruling, one way or another.
Ghaz wrote:And you haven't explained how a power weapon that says it works on models wounded in close combat when you're not in close combat.
This is not an unreasonable point. I would say the sense in which they are not directly comparable is that if we ignore the ability to deny armor saves the power weapon is meaningless. Whereas if we ignore the ability to do the "boom", the empathic obliterator is still doing something. Beyond that, the additional steps required to activate the "boom" seem at least to imply that the intent is for it only to go off when locked in close combat. I suspect it is worth a
FAQ, as it's not 100% obvious, by any means.