I think Jim said it pretty well. They put the cart before the horse, the cart being DLC and the horse being the actual game.
Offer a complete game now, offer the DLC later. Don't offer the DLC before the first screenshot of the game is even available, and DON'T offer day-one DLC. Pre-orders are the enemy of consumers. If they truly intended to be consumer-friendly, they made really a lousy first impression. Still, to be fair, the rottenness of pre-orders is lessened a bit by the fact that the beta is available for play, meaning it's not a completely blind purchase.
Lots of people were really impressed with the beta of the game, which had none of this DLC. Presenting the DLC right now makes it look like that stuff COULD be in the game, but won't be because it could be bought as DLC instead. Presenting it later at least suggests that it was an idea conceived after the game was released.