And confirmed here that you will in fact have to buy the game 3 times if you want to play all three campaigns.
To put it simply: this is bullshit. Fuck Blizzard.
I'm sure they could sell each one for $15-20 but I have the funny feeling the first one is going to be sold for $40-50 and then next two 'expansions' will be $15-20 each.
It's like they want people to pirate their game.