If they do - or you have direct access to them - could you ask them personally what they think is added to the game, by not being able to defend vassals. I've played some games in my time before, but this vassal tennis, where one person takes a vassal, you take it back, they then take it again, you take it back ad infinitum. I could bore you with the hundreds of times this has happened, but I wont put you through it - I just wondered why they thought putting players through this monotony was ever going to help the gameplay. Somebody, somewhere must have come up with this idea, and I am intrigued as to what logic he was using when he came up with it. When a game of strategy turns into a battle of boredom - whoever gets bored the quickest will end up losing - I don't feel it helps things.
Sorry, no more time to type - have to get back to the game - coz every 10 minutes I need to take my vassals back