Then I read an article about The Coin on OP's blog: http://buddypanda.com/?p=65 and I don't think that the simulator is that useful. Maybe I'm too dumb to understand this, but my intuitive idea is that a card like The Coin gives you various advantages and no disadvantages, since it is an extra card that comes for free and gives you more flexibility. How come then, that the simulator says that the player actually wins more games without The Coin?
Hearthstone isn't mainly about random encounters between AI opponents, but to gain advantage in material over your opponent over the course of the game. Sometimes, 1hp, 1 card, 1 round is sufficient to decide over victory or defeat. If the simulator neglects hero abilities (as in The Coin article), my guess would be that it's not too accurate.
However, I thought that a simulator for Hearthstone would be a great idea. I think you're onto something here, but I'd like to see a few more use cases that match my intuition I gained from playing hundreds of games of Hearthstone.