One thing you guys are forgetting is that next year MM is getting a movie, (I think, not sure about that) and Batman is getting a video game, so I would think LEGO would try to get a few more bucks with the lines.
Hear me out on this, I think without these, the 2 lines would have ended already, my guess is that they planned these a year ago, and were forced to continue the lines a bit longer to time them with the movie and video game.
As for the castle line, they might have it for 2008, but my guess is that in 2009 they'll make the "farewell" sets :-P