Indeed.
The Abyss is the ruler of the Abyss.
I've always viewed the Abyssal Lords as having a more primal connection to the Abyss, being more in tune with its true nature and the influence of its malevolent Xaos incarnate. True deities on the other hand have distanced themselves from any connection they might have had with the plane they've carved out a domain on. They're no longer listening to the plane, or they no longer can, as they're far too busy listening to their own mortal worshippers. True deities just have totally different concerns, they're molded by the belief of their flock, and ultimately dependant on that worship.
True deities are removed from the normal politics of the Abyss for the most part for various reasons, and by virtue of concern, care, or enlightened self-interest, deities in the Abyss don't interfere with the Abyssal Lords, and the Abyssal Lords largely avoid those deities.