First off, sorry for further derailing this post, but the original issue is pretty much answered and damiekpe makes some good questions I just can't resist answering.

Besides giving you the conquered land, Crusades will also give you money and Fame upon completion of your objective. Furthermore your Generals that go on Crusade can earn unique Crusader virtues. So I think they added a real motivation for going on Crusade. In M:TW there was no reason to go on Crusade, because frankly your money was better invested in conquering some neighbouring provinces. With the M2:TW system I might even find myself going on the Crusades for gameplay reasons and not because I think it's fun to replay history as a Crusaders army.