A friend of mine noticed that the Greater Combat Maneuver feats, e.g. Greater Bull Rush, do not add +2 to the CMD, whether it be an alteration or continuous oversight on our part.
I believe the confusion comes in from the mentality of "if a weapon gets a bonus towards CMB, it gets the same bonus to CMD."
At any rate, I thought this inconsistency may be worth mentioning in the event someone else presumed this to be the case.