The stacking of Autarchs is an advantage for the Eldar army that forces them to take both HQs up with sub-par choices. Plus Eldar don't have near as many units that take advantage of special Reserve rules as IG does. So it's much less useful.
Taking two Command HQs has myriad other advantages and is in no way hamstringing the IG list. Also it would be worse if the Astropath stacked (advantage for IG) and the Fleet Officer didn't (which would royally fuck Daemons and Drop type armies).
So one helps just their own army and the other has the potential to make it a non-game for the enemy. Which would suck.
Strange, but not a Stranger.