I just picked up the core set and in reading the rules for set up, after the players pick out their decks, play their plot cards, it said that they then choose their house card. It is my understanding that they've already chosen their house and deck at this point so is there more house cards per house available in the expansions or am I misunderstanding something?

Bataar said:

Well, what it really says is that first you separate your plot deck from your House deck. You haven't actually played anything yet. Then, players indicate which House card (and Agenda, if applicable) they are playing. Indicating which House you are playing is not really the same thing as "choosing" your House. Sure, you have already chosen which House you are going to play when you put the deck together, but this is the first point in the game when your opponents get to know what House you are going to play.

What you may be misunderstanding is that the rules encompass a lot more than just the 4 decks that come pre-made in the Core Set. If all you ever do is play those 4 decks, essentially setting them down in the middle for each player to pick up, then yes, this part of setup is pretty redundant and doesn't carry any specific meaning or action. But if you are customizing your decks, so that everyone is playing with decks they put together and brought with them (instead of using the 4 decks "out of the box"), then you aren't going to know, when you sit down, who is playing what. That entry does say that more than one player can have the same House - something that isn't going to happen if you play with the 4 decks "as is" in the Core Set.