I assure you, I have a problem with Hearthstone.
But to address your specific point, the difference is in shoehorning gambling into the core gameplay. Hearthstone is built on a card game concept that relies on gambling, for better or worse, within the scope of the game. There is a 'rarity market' in CCGs/TCGs that is part of the complexity and fun of the environment, this is why 'Proxy MTG' is simply not that interesting to your average person.
This game has a model that is clearly defined and exists everywhere in established rules without a slot machine attached to power and advancement. It's not 'the way you play the game', in the same way that you don't have to run through a slot machine system to assemble a deck of cards to play poker, though you could certainly try to add one.
I also just have a problem with the pricing schemes of a lot of these games. I don't really agree with digital CCG pricing either, but there are few good ones to complain about and the religious cult of Hearthstone insulates the wider audience from any criticism.