I wonder what the numbers were when they released the final LK raid where you fought the LK, I bet the subscription base was at its all time high. I have to speculate if it will reach that at the end raid for Cat, as Deathwing is not as interesting as the final chapter of the fall of Arthas was.
One of the reasons I feel they are holding back content is because of the new Star Wars mmo, when that ships, watch a huge content patch get dropped.