Anyone who's got this far in the thread would appreciate, or will already have appreciated, the first few pages of Resencrantz and Gildernstern are Dead (as well as the rest of the play) by Tom Stoppard. Priceless.

Marian, whether the house has prior knowledge about the cups is not a factor, except that if the prize cup is turned over, you lose your chance to reconsider. I know you didn't appreciate Jim's line on this, but it does help at the intuition level, so I'll use that to explain. Suppose the house invites you to pick the Ace of Spades out of a face-down pack of cards. You take a card but don't look at it. The house then turns over all but one of the remaining cards, without turning up the Ace of Spades. The house is not likely to achieve this feat without prior knowledge, but theoretically could. With or without prior knowledge, the house has made a dramatic intervention, which statistically you'd be daft to ignore.

When you picked your card, there were fity-one to one chances that the house still had the Ace of Spades. Nothing's changed, except that those 51 to one chances are now vested in the one remained face-down card held by the house.

The prisoner analogy has no bearing on the three-cup problem as no-one got to have a guess before the house intervened and changed the odds.